diff --git a/middleman-core/lib/middleman-core/application.rb b/middleman-core/lib/middleman-core/application.rb
index b65c05fe..ea98a17d 100644
--- a/middleman-core/lib/middleman-core/application.rb
+++ b/middleman-core/lib/middleman-core/application.rb
@@ -44,69 +44,69 @@ module Middleman
 
     # Root project directory (overwritten in middleman build/server)
     # @return [String]
-    set :root,        ENV["MM_ROOT"] || Dir.pwd
+    config.define_setting :root, (ENV["MM_ROOT"] || Dir.pwd), 'Root project directory'
 
     # Pathname-addressed root
     def self.root_path
-      Pathname(root)
+      Pathname(config[:root])
     end
     delegate :root_path, :to => :"self.class"
 
     # Name of the source directory
     # @return [String]
-    set :source,      "source"
+    config.define_setting :source,      "source", 'Name of the source directory'
 
     # Middleman environment. Defaults to :development, set to :build by the build process
     # @return [String]
-    set :environment, (ENV['MM_ENV'] && ENV['MM_ENV'].to_sym) || :development
+    config.define_setting :environment, ((ENV['MM_ENV'] && ENV['MM_ENV'].to_sym) || :development), 'Middleman environment. Defaults to :development, set to :build by the build process'
 
     # Which file should be used for directory indexes
     # @return [String]
-    set :index_file,  "index.html"
+    config.define_setting :index_file,  "index.html", 'Which file should be used for directory indexes'
 
     # Whether to strip the index file name off links to directory indexes
     # @return [Boolean]
-    set :strip_index_file, true
+    config.define_setting :strip_index_file, true, 'Whether to strip the index file name off links to directory indexes'
 
     # Whether to include a trailing slash when stripping the index file
     # @return [Boolean]
-    set :trailing_slash, true
+    config.define_setting :trailing_slash, true, 'Whether to include a trailing slash when stripping the index file'
 
     # Location of javascripts within source.
     # @return [String]
-    set :js_dir,      "javascripts"
+    config.define_setting :js_dir,      "javascripts", 'Location of javascripts within source'
 
     # Location of stylesheets within source. Used by Compass.
     # @return [String]
-    set :css_dir,     "stylesheets"
+    config.define_setting :css_dir,     "stylesheets", 'Location of stylesheets within source'
 
     # Location of images within source. Used by HTML helpers and Compass.
     # @return [String]
-    set :images_dir,  "images"
+    config.define_setting :images_dir,  "images", 'Location of images within source'
 
     # Location of fonts within source. Used by Compass.
     # @return [String]
-    set :fonts_dir,   "fonts"
+    config.define_setting :fonts_dir,   "fonts", 'Location of fonts within source'
 
     # Where to build output files
     # @return [String]
-    set :build_dir,   "build"
+    config.define_setting :build_dir,   "build", 'Where to build output files'
 
     # Default prefix for building paths. Used by HTML helpers and Compass.
     # @return [String]
-    set :http_prefix, "/"
+    config.define_setting :http_prefix, "/", 'Default prefix for building paths'
 
     # Default string encoding for templates and output.
     # @return [String]
-    set :encoding,    "utf-8"
+    config.define_setting :encoding,    "utf-8", 'Default string encoding for templates and output'
 
     # Whether to catch and display exceptions
     # @return [Boolean]
-    set :show_exceptions, true
+    config.define_setting :show_exceptions, true, 'Whether to catch and display exceptions'
 
     # Default layout name
     # @return [String, Symbold]
-    set :layout, :_auto_layout
+    config.define_setting :layout, :_auto_layout, 'Default layout name'
 
     # Activate custom features and extensions
     include Middleman::CoreExtensions::Extensions
@@ -151,12 +151,12 @@ module Middleman
       cache.clear
 
       # Setup the default values from calls to set before initialization
-      self.class.superclass.config.to_h.each { |k,v| self.class.set(k,v) }
+      self.class.superclass.config.to_h.each { |k,v| self.class.config.define_setting(k,v) }
 
       # Evaluate a passed block if given
       instance_exec(&block) if block_given?
 
-      set :source, ENV["MM_SOURCE"] if ENV["MM_SOURCE"]
+      config[:source] = ENV["MM_SOURCE"] if ENV["MM_SOURCE"]
 
       super
     end
@@ -172,17 +172,17 @@ module Middleman
 
     # Whether we're in development mode
     # @return [Boolean] If we're in dev mode
-    def development?; environment == :development; end
+    def development?; config[:environment] == :development; end
 
     # Whether we're in build mode
     # @return [Boolean] If we're in build mode
-    def build?; environment == :build; end
+    def build?; config[:environment] == :build; end
 
     # The full path to the source directory
     #
     # @return [String]
     def source_dir
-      File.join(root, source)
+      File.join(config[:root], config[:source])
     end
 
     delegate :logger, :instrument, :to => ::Middleman::Util
@@ -205,7 +205,7 @@ module Middleman
 
       if !resource
         # Try it with /index.html at the end
-        indexed_path = File.join(path.sub(%r{/$}, ''), index_file)
+        indexed_path = File.join(path.sub(%r{/$}, ''), config[:index_file])
         resource = sitemap.find_resource_by_destination_path(indexed_path)
       end
 
diff --git a/middleman-core/lib/middleman-core/cli/build.rb b/middleman-core/lib/middleman-core/cli/build.rb
index 7ec7a558..861c6458 100644
--- a/middleman-core/lib/middleman-core/cli/build.rb
+++ b/middleman-core/lib/middleman-core/cli/build.rb
@@ -83,7 +83,7 @@ module Middleman::Cli
       # @return [Middleman::Application]
       def shared_instance(verbose=false, instrument=false)
         @_shared_instance ||= ::Middleman::Application.server.inst do
-          set :environment, :build
+          config[:environment] = :build
           logger(verbose ? 0 : 1, instrument)
         end
       end
diff --git a/middleman-core/lib/middleman-core/configuration.rb b/middleman-core/lib/middleman-core/configuration.rb
index 4ee8211a..6cede94d 100644
--- a/middleman-core/lib/middleman-core/configuration.rb
+++ b/middleman-core/lib/middleman-core/configuration.rb
@@ -30,7 +30,7 @@ module Middleman
         # old Middleman.
         #
         # @deprecated Prefer accessing settings through "config".
-        def method_missing(method)
+        def method_missing(method, *args)
           if config.defines_setting? method
             config[method]
           else
@@ -71,7 +71,7 @@ module Middleman
       # old Middleman.
       #
       # @deprecated Prefer accessing settings through "config".
-      def method_missing(method)
+      def method_missing(method, *args)
         if config.defines_setting? method
           config[method]
         else
@@ -128,7 +128,7 @@ module Middleman
         if defines_setting?(method) && args.size == 0
           self[method]
         elsif method =~ /^(\w+)=$/ && args.size == 1
-          self[$1] = args[0]
+          self[$1.to_sym] = args[0]
         else
           super
         end
@@ -190,9 +190,17 @@ module Middleman
       end
     end
 
+    # An individual configuration setting, with an optional default and description.
+    # Also models whether or not a value has been set.
     class ConfigSetting
-      attr_accessor :key, :default, :description
-      attr_writer :value
+      # The name of this setting
+      attr_accessor :key
+
+      # The default value for this setting
+      attr_accessor :default
+
+      # A human-friendly description of the setting
+      attr_accessor :description
 
       def initialize(key, default, description)
         @value_set = false
@@ -201,15 +209,20 @@ module Middleman
         self.description = description
       end
 
+      # The user-supplied value for this setting, overriding the default
       def value=(value)
         @value = value
         @value_set = true
       end
 
+      # The effective value of the setting, which may be the default
+      # if the user has not set a value themselves. Note that even if the
+      # user sets the value to nil it will override the default.
       def value
         value_set? ? @value : default
       end
 
+      # Whether or not there has been a value set beyond the default
       def value_set?
         @value_set
       end
diff --git a/middleman-core/lib/middleman-core/core_extensions/data.rb b/middleman-core/lib/middleman-core/core_extensions/data.rb
index 360d953f..bc2778af 100644
--- a/middleman-core/lib/middleman-core/core_extensions/data.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/data.rb
@@ -13,7 +13,7 @@ module Middleman
           require "yaml"
           require "active_support/json"
 
-          app.set :data_dir, "data"
+          app.config.define_setting :data_dir, "data", "The directory data files are stored in"
           app.send :include, InstanceMethods
         end
         alias :included :registered
@@ -24,12 +24,12 @@ module Middleman
         # Setup data files before anything else so they are available when
         # parsing config.rb
         def initialize
-          self.files.changed DataStore.matcher do |file|
-            self.data.touch_file(file) if file.match(%r{^#{self.data_dir}\/})
+          files.changed DataStore.matcher do |file|
+            data.touch_file(file) if file.match(%r{^#{config[:data_dir]}\/})
           end
 
-          self.files.deleted DataStore.matcher do |file|
-            self.data.remove_file(file) if file.match(%r{^#{self.data_dir}\/})
+          files.deleted DataStore.matcher do |file|
+            data.remove_file(file) if file.match(%r{^#{config[data_dir]}\/})
           end
 
           super
diff --git a/middleman-core/lib/middleman-core/core_extensions/extensions.rb b/middleman-core/lib/middleman-core/core_extensions/extensions.rb
index 9f77b510..3f8d1d01 100644
--- a/middleman-core/lib/middleman-core/core_extensions/extensions.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/extensions.rb
@@ -42,11 +42,8 @@ module Middleman
           app.define_hook :build_config
           app.define_hook :development_config
 
-          if ENV["AUTOLOAD_SPROCKETS"]
-            app.set :autoload_sprockets, (ENV["AUTOLOAD_SPROCKETS"] == "true")
-          else
-            app.set :autoload_sprockets, true
-          end
+          app.config.define_setting :autoload_sprockets, true, 'Automatically load sprockets at startup?'
+          app.config[:autoload_sprockets] = (ENV["AUTOLOAD_SPROCKETS"] == "true") if ENV["AUTOLOAD_SPROCKETS"]
 
           app.extend ClassMethods
           app.send :include, InstanceMethods
@@ -134,7 +131,7 @@ module Middleman
             instance_eval File.read(local_config), local_config, 1
           end
 
-          if autoload_sprockets
+          if config[:autoload_sprockets]
             begin
               require "middleman-sprockets"
               activate(:sprockets)
diff --git a/middleman-core/lib/middleman-core/core_extensions/external_helpers.rb b/middleman-core/lib/middleman-core/core_extensions/external_helpers.rb
index 0f2118ea..3e4716b0 100644
--- a/middleman-core/lib/middleman-core/core_extensions/external_helpers.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/external_helpers.rb
@@ -9,20 +9,20 @@ module Middleman
         # once registered
         def registered(app)
           # Setup a default helpers paths
-          app.set :helpers_dir, "helpers"
-          app.set :helpers_filename_glob, "**{,/*/**}/*.rb"
-          app.set :helpers_filename_to_module_name_proc, Proc.new { |filename|
+          app.config.define_setting :helpers_dir, "helpers", 'Directory to autoload helper modules from'
+          app.config.define_setting :helpers_filename_glob, "**.rb", 'Glob pattern for matching helper ruby files'
+          app.config.define_setting :helpers_filename_to_module_name_proc, Proc.new { |filename|
             basename = File.basename(filename, File.extname(filename))
             basename.camelcase
-          }
+          }, 'Proc implementing the conversion from helper filename to module name'
 
           # After config
           app.after_configuration do
-            helpers_path = File.expand_path(helpers_dir, root)
+            helpers_path = File.expand_path(config[:helpers_dir], config[:root])
             next unless File.exists?(helpers_path)
 
-            Dir[File.join(helpers_path, helpers_filename_glob)].each do |filename|
-              module_name = helpers_filename_to_module_name_proc.call(filename)
+            Dir[File.join(helpers_path, config[:helpers_filename_glob])].each do |filename|
+              module_name = config[:helpers_filename_to_module_name_proc].call(filename)
               next unless module_name
 
               require filename
diff --git a/middleman-core/lib/middleman-core/core_extensions/rendering.rb b/middleman-core/lib/middleman-core/core_extensions/rendering.rb
index cfca198f..3e040564 100644
--- a/middleman-core/lib/middleman-core/core_extensions/rendering.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/rendering.rb
@@ -257,7 +257,7 @@ module Middleman
             extension_class = ::Tilt[ext]
             ::Tilt.mappings.each do |ext, engines|
               next unless engines.include? extension_class
-              engine_options = respond_to?(ext.to_sym) ? send(ext.to_sym) : {}
+              engine_options = config[ext.to_sym] || {}
               options.merge!(engine_options)
             end
 
diff --git a/middleman-core/lib/middleman-core/core_extensions/routing.rb b/middleman-core/lib/middleman-core/core_extensions/routing.rb
index db7c6e61..0416fec1 100644
--- a/middleman-core/lib/middleman-core/core_extensions/routing.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/routing.rb
@@ -30,10 +30,10 @@ module Middleman
         def with_layout(layout_name, &block)
           old_layout = layout
 
-          set :layout, layout_name
+          config[:layout] = layout_name
           instance_exec(&block) if block_given?
         ensure
-          set :layout, old_layout
+          config[:layout] = old_layout
         end
 
         # The page method allows the layout to be set on a specific path
diff --git a/middleman-core/lib/middleman-core/preview_server.rb b/middleman-core/lib/middleman-core/preview_server.rb
index 2d6f187d..0d6b3bec 100644
--- a/middleman-core/lib/middleman-core/preview_server.rb
+++ b/middleman-core/lib/middleman-core/preview_server.rb
@@ -71,7 +71,7 @@ module Middleman
         opts = @options
         @app =::Middleman::Application.server.inst do
           if opts[:environment]
-            set :environment, opts[:environment].to_sym
+            config[:environment] = opts[:environment].to_sym
           end
           
           logger(opts[:debug] ? 0 : 1, opts[:instrumenting] || false)
diff --git a/middleman-core/lib/middleman-core/renderers/erb.rb b/middleman-core/lib/middleman-core/renderers/erb.rb
index 6ae858bb..e6a6f6b6 100644
--- a/middleman-core/lib/middleman-core/renderers/erb.rb
+++ b/middleman-core/lib/middleman-core/renderers/erb.rb
@@ -8,8 +8,8 @@ module Middleman
         # once registered
         def registered(app)
           # Setup a default ERb engine
-          app.set :erb_engine, :erb
-          app.set :erb_engine_prefix, ::Tilt
+          app.config.define_setting :erb_engine, :erb, 'The engine to use for rendering ERb templates'
+          app.config.define_setting :erb_engine_prefix, ::Tilt, 'The parent module for ERb template engines'
 
           app.before_configuration do
             template_extensions :erb => :html
@@ -19,14 +19,14 @@ module Middleman
           app.after_configuration do
             # Find the user's prefered engine
             # Convert symbols to classes
-            if erb_engine.is_a? Symbol
+            if config[:erb_engine].is_a? Symbol
               engine = engine.to_s
               engine = engine == "erb" ? "ERB" : engine.camelize
-              erb_engine = erb_engine_prefix.const_get("#{engine}Template")
+              config[:erb_engine] = config[:erb_engine_prefix].const_get("#{engine}Template")
             end
 
             # Tell Tilt to use the preferred engine
-            ::Tilt.prefer(erb_engine)
+            ::Tilt.prefer(config[:erb_engine])
           end
         end
         alias :included :registered
diff --git a/middleman-core/lib/middleman-core/renderers/less.rb b/middleman-core/lib/middleman-core/renderers/less.rb
index b4382d6d..5f789980 100644
--- a/middleman-core/lib/middleman-core/renderers/less.rb
+++ b/middleman-core/lib/middleman-core/renderers/less.rb
@@ -11,8 +11,8 @@ module Middleman
 
         # Once registered
         def registered(app)
-          # Default sass options
-          app.set :less, {}
+          # Default less options
+          app.config.define_setting :less, {}, 'LESS compiler options'
 
           app.before_configuration do
             template_extensions :less => :css
diff --git a/middleman-core/lib/middleman-core/renderers/markdown.rb b/middleman-core/lib/middleman-core/renderers/markdown.rb
index ae2dd78c..06d017cb 100644
--- a/middleman-core/lib/middleman-core/renderers/markdown.rb
+++ b/middleman-core/lib/middleman-core/renderers/markdown.rb
@@ -10,8 +10,8 @@ module Middleman
         # Once registered
         def registered(app)
           # Set our preference for a markdown engine
-          app.set :markdown_engine, :maruku
-          app.set :markdown_engine_prefix, ::Tilt
+          app.config.define_setting :markdown_engine, :maruku, 'Preferred markdown engine'
+          app.config.define_setting :markdown_engine_prefix, ::Tilt, 'The parent module for markdown template engines'
 
           app.before_configuration do
             template_extensions :markdown => :html,
@@ -26,24 +26,24 @@ module Middleman
 
             begin
               # Look for the user's preferred engine
-              if markdown_engine == :redcarpet
+              if config[:markdown_engine] == :redcarpet
                 require "middleman-core/renderers/redcarpet"
                 ::Tilt.prefer(::Middleman::Renderers::RedcarpetTemplate)
-              elsif !markdown_engine.nil?
+              elsif !config[:markdown_engine].nil?
                 # Map symbols to classes
-                markdown_engine_klass = if markdown_engine.is_a? Symbol
-                  engine = markdown_engine.to_s
+                markdown_engine_klass = if config[:markdown_engine].is_a? Symbol
+                  engine = config[:markdown_engine].to_s
                   engine = engine == "rdiscount" ? "RDiscount" : engine.camelize
-                  markdown_engine_prefix.const_get("#{engine}Template")
+                  config[:markdown_engine_prefix].const_get("#{engine}Template")
                 else
-                  markdown_engine_prefix
+                  config[:markdown_engine_prefix]
                 end
 
                 # Tell tilt to use that engine
                 ::Tilt.prefer(markdown_engine_klass)
               end
             rescue LoadError
-              logger.warn "Requested Markdown engine (#{markdown_engine}) not found. Maybe the gem needs to be installed and required?"
+              logger.warn "Requested Markdown engine (#{config[:markdown_engine]}) not found. Maybe the gem needs to be installed and required?"
             end
           end
         end
diff --git a/middleman-core/lib/middleman-core/renderers/sass.rb b/middleman-core/lib/middleman-core/renderers/sass.rb
index c77ff611..38b6afa1 100644
--- a/middleman-core/lib/middleman-core/renderers/sass.rb
+++ b/middleman-core/lib/middleman-core/renderers/sass.rb
@@ -12,16 +12,16 @@ module Middleman
         # Once registered
         def registered(app)
           # Default sass options
-          app.set :sass, {}
+          app.config.define_setting :sass, {}, 'Sass engine options'
 
           # Location of SASS .sass_cache directory.
           # @return [String]
-          #   set :sass_cache_path, "/tmp/middleman-app-name/sass_cache"
-          app.set(:sass_cache_path) { File.join(app.root_path, '.sass_cache') } # runtime compile of path
+          app.config.define_setting :sass_cache_path, nil, 'Location of sass cache' # runtime compile of path
 
           app.before_configuration do
             template_extensions :scss => :css,
                                 :sass => :css
+            config[:sass_cache_path] = File.join(app.root_path, '.sass_cache')
           end
 
           # Tell Tilt to use it as well (for inline sass blocks)
@@ -76,11 +76,11 @@ module Middleman
           more_opts = { :filename => eval_file, :line => line, :syntax => syntax }
           
           if @context.is_a?(::Middleman::Application) && file
-            location_of_sass_file = File.expand_path(@context.source, @context.root)
+            location_of_sass_file = @context.source_dir
           
             parts = basename.split('.')
             parts.pop
-            more_opts[:css_filename] = File.join(location_of_sass_file, @context.css_dir, parts.join("."))
+            more_opts[:css_filename] = File.join(location_of_sass_file, @context.config[:css_dir], parts.join("."))
           end
           
           options.merge(more_opts)
diff --git a/middleman-core/lib/middleman-core/sitemap.rb b/middleman-core/lib/middleman-core/sitemap.rb
index 3b7c3ef1..a5693630 100644
--- a/middleman-core/lib/middleman-core/sitemap.rb
+++ b/middleman-core/lib/middleman-core/sitemap.rb
@@ -20,10 +20,10 @@ module Middleman
         app.register Middleman::Sitemap::Extensions::Ignores
 
         # Set to automatically convert some characters into a directory
-        app.set :automatic_directory_matcher, nil
+        app.config.define_setting :automatic_directory_matcher, nil, 'Set to automatically convert some characters into a directory'
 
         # Setup callbacks which can exclude paths from the sitemap
-        app.set :ignored_sitemap_matchers, {
+        app.config.define_setting :ignored_sitemap_matchers, {
           # dotfiles and folders in the root
           :root_dotfiles => proc { |file| file.match(%r{^\.}) },
 
@@ -38,7 +38,7 @@ module Middleman
           :layout => proc { |file|
             file.match(%r{^source/layout\.}) || file.match(%r{^source/layouts/})
           }
-        }
+        }, 'Callbacks that can exclude paths from the sitemap'
 
         # Include instance methods
         app.send :include, InstanceMethods
diff --git a/middleman-core/lib/middleman-core/templates/extension/lib/lib.rb b/middleman-core/lib/middleman-core/templates/extension/lib/lib.rb
index a2459194..1eb1796c 100644
--- a/middleman-core/lib/middleman-core/templates/extension/lib/lib.rb
+++ b/middleman-core/lib/middleman-core/templates/extension/lib/lib.rb
@@ -7,9 +7,6 @@ module MyExtension
 
     # Called when user `activate`s your extension
     def registered(app, options={})
-      # Setup extension-specific config
-      app.set :config_variable, false
-
       # Include class methods
       # app.extend ClassMethods
 
@@ -18,9 +15,6 @@ module MyExtension
 
       app.after_configuration do
         # Do something
-
-        # config_variable is now either the default or the user's
-        # setting from config.rb
       end
     end
     alias :included :registered
diff --git a/middleman-more/lib/middleman-more/core_extensions/assets.rb b/middleman-more/lib/middleman-more/core_extensions/assets.rb
index 13fb0a6f..8fdde3ca 100644
--- a/middleman-more/lib/middleman-more/core_extensions/assets.rb
+++ b/middleman-more/lib/middleman-more/core_extensions/assets.rb
@@ -33,7 +33,7 @@ module Middleman
             if resource = sitemap.find_resource_by_path(path)
               resource.url
             else
-              File.join(http_prefix, path)
+              File.join(config[:http_prefix], path)
             end
           end
         end
diff --git a/middleman-more/lib/middleman-more/core_extensions/compass.rb b/middleman-more/lib/middleman-more/core_extensions/compass.rb
index 2f9f98dd..78b7d13f 100644
--- a/middleman-more/lib/middleman-more/core_extensions/compass.rb
+++ b/middleman-more/lib/middleman-more/core_extensions/compass.rb
@@ -19,38 +19,38 @@ module Middleman
 
           # Location of SASS/SCSS files external to source directory.
           # @return [Array]
-          #   set :sass_assets_paths, ["#{root}/assets/sass/", "/path/2/external/sass/repository/"]
-          app.set :sass_assets_paths, []
+          #   config[:sass_assets_paths] = ["#{root}/assets/sass/", "/path/2/external/sass/repository/"]
+          app.config.define_setting :sass_assets_paths, [], 'Paths to extra SASS/SCSS files'
 
           app.after_configuration do
-            ::Compass.configuration do |config|
-              config.project_path    = source_dir
-              config.environment     = :development
-              config.cache_path      = sass_cache_path
-              config.sass_dir        = css_dir
-              config.additional_import_paths = sass_assets_paths
-              config.css_dir         = css_dir
-              config.javascripts_dir = js_dir
-              config.fonts_dir       = fonts_dir
-              config.images_dir      = images_dir
-              config.http_path       = http_prefix
+            ::Compass.configuration do |compass_config|
+              compass_config.project_path    = source_dir
+              compass_config.environment     = :development
+              compass_config.cache_path      = config[:sass_cache_path]
+              compass_config.sass_dir        = config[:css_dir]
+              compass_config.additional_import_paths = config[:sass_assets_paths]
+              compass_config.css_dir         = config[:css_dir]
+              compass_config.javascripts_dir = config[:js_dir]
+              compass_config.fonts_dir       = config[:fonts_dir]
+              compass_config.images_dir      = config[:images_dir]
+              compass_config.http_path       = config[:http_prefix]
 
               # Disable this initially, the cache_buster extension will
               # re-enable it if requested.
-              config.asset_cache_buster :none
+              compass_config.asset_cache_buster :none
 
               # Disable this initially, the relative_assets extension will
               # re-enable it if requested.
-              config.relative_assets = false
+              compass_config.relative_assets = false
 
               # Default output style
-              config.output_style = :nested
+              compass_config.output_style = :nested
 
               # No line-comments in test mode (changing paths mess with sha1)
-              config.line_comments = false if ENV["TEST"]
+              compass_config.line_comments = false if ENV["TEST"]
 
-              if respond_to?(:asset_host) && asset_host.is_a?(Proc)
-                config.asset_host(&asset_host)
+              if config.defines_setting?(:asset_host) && config[:asset_host].is_a?(Proc)
+                compass_config.asset_host(&config[:asset_host])
               end
             end
 
diff --git a/middleman-more/lib/middleman-more/core_extensions/default_helpers.rb b/middleman-more/lib/middleman-more/core_extensions/default_helpers.rb
index b9b5076e..f9b66cb6 100644
--- a/middleman-more/lib/middleman-more/core_extensions/default_helpers.rb
+++ b/middleman-more/lib/middleman-more/core_extensions/default_helpers.rb
@@ -20,7 +20,7 @@ module Middleman
 
           app.helpers Helpers
 
-          app.set :relative_links, false
+          app.config.define_setting :relative_links, false, 'Whether to generate relative links instead of absolute ones'
         end
         alias :included :registered
       end
@@ -110,7 +110,7 @@ module Middleman
         # :relative option which, if set to true, will produce
         # relative URLs instead of absolute URLs. You can also add
         #
-        # set :relative_links, true
+        # config[:relative_links] = true
         #
         # to config.rb to have all links default to relative.
         def link_to(*args, &block)
@@ -136,10 +136,10 @@ module Middleman
 
               resource = sitemap.find_resource_by_path(url)
 
-              # Allow people to turn on relative paths for all links with set :relative_links, true
+              # Allow people to turn on relative paths for all links with config[:relative_links] = true
               # but still override on a case by case basis with the :relative parameter.
               effective_relative = relative || false
-              if relative.nil? && relative_links
+              if relative.nil? && config[:relative_links]
                 effective_relative = true
               end
 
diff --git a/middleman-more/lib/middleman-more/core_extensions/i18n.rb b/middleman-more/lib/middleman-more/core_extensions/i18n.rb
index eb23e70f..d0f6d80b 100644
--- a/middleman-more/lib/middleman-more/core_extensions/i18n.rb
+++ b/middleman-more/lib/middleman-more/core_extensions/i18n.rb
@@ -9,11 +9,11 @@ module Middleman
 
         # Once registerd
         def registered(app, options={})
-          app.set :locales_dir, "locales"
+          app.config.define_setting :locales_dir, "locales", 'The directory holding your locale configurations'
 
           # Needed for helpers as well
           app.after_configuration do
-            locales_glob = File.join(locales_dir, "*.yml");
+            locales_glob = File.join(config[:locales_dir], "*.yml");
 
             ::I18n.load_path += Dir[File.join(root, locales_glob)]
             ::I18n.reload!
diff --git a/middleman-more/lib/middleman-more/extensions/asset_host.rb b/middleman-more/lib/middleman-more/extensions/asset_host.rb
index 0cddce83..d43e9a39 100644
--- a/middleman-more/lib/middleman-more/extensions/asset_host.rb
+++ b/middleman-more/lib/middleman-more/extensions/asset_host.rb
@@ -11,7 +11,7 @@ module Middleman
         # Once registered
         def registered(app)
           # Default to no host
-          app.set :asset_host, false
+          app.config.define_setting :asset_host, false, 'The asset host to use, or false for no asset host, or a Proc to determine asset host'
 
           # Include methods
           app.send :include, InstanceMethods
@@ -30,12 +30,12 @@ module Middleman
         # @return [String]
         def asset_url(path, prefix="")
           original_output = super
-          return original_output unless asset_host
+          return original_output unless config[:asset_host]
 
-          asset_prefix = if asset_host.is_a?(Proc)
-            asset_host.call(original_output)
-          elsif asset_host.is_a?(String)
-            asset_host
+          asset_prefix = if config[:asset_host].is_a?(Proc)
+            config[:asset_host].call(original_output)
+          elsif config[:asset_host].is_a?(String)
+            config[:asset_host]
           end
 
           File.join(asset_prefix, original_output)
diff --git a/middleman-more/lib/middleman-more/extensions/minify_css.rb b/middleman-more/lib/middleman-more/extensions/minify_css.rb
index ac4b9644..d4f4bed0 100644
--- a/middleman-more/lib/middleman-more/extensions/minify_css.rb
+++ b/middleman-more/lib/middleman-more/extensions/minify_css.rb
@@ -10,13 +10,13 @@ module Middleman
 
         # Once registered
         def registered(app, options={})
-          app.set :css_compressor, false
+          app.config.define_setting :css_compressor, nil, 'Set the CSS compressor to use. Deprecated in favor of the :compressor option when activating :minify_css'
 
           ignore = Array(options[:ignore]) << /\.min\./
           inline = options[:inline] || false
 
           app.after_configuration do
-            chosen_compressor = css_compressor || options[:compressor] || begin
+            chosen_compressor = config[:css_compressor] || options[:compressor] || begin
               require "middleman-more/extensions/minify_css/rainpress"
               ::Rainpress
             end
diff --git a/middleman-more/lib/middleman-more/extensions/minify_javascript.rb b/middleman-more/lib/middleman-more/extensions/minify_javascript.rb
index 5ffae15c..9a1e91e6 100644
--- a/middleman-more/lib/middleman-more/extensions/minify_javascript.rb
+++ b/middleman-more/lib/middleman-more/extensions/minify_javascript.rb
@@ -10,7 +10,7 @@ module Middleman
 
         # Once registered
         def registered(app, options={})
-          app.set :js_compressor, false
+          app.config.define_setting :js_compressor, nil, 'Set the JS compressor to use. Deprecated in favor of the :compressor option when activating :minify_js'
 
           ignore = Array(options[:ignore]) << /\.min\./
           inline = options[:inline] || false