Files with "+"s in their names (e.g. from Wiki pages with spaces in their names) were not being expired properly. This is actually a Rails bug, but I fixed it by patching the action_cache plugin.
Added the action_cache plugin
http://agilewebdevelopment.com/plugins/action_cache
which does action-caching with ETags support. The built-in Rails ETags "solution" sucks, because it forces a page-rerender, even when the content is unchanged.
Jacques Distler