Sessions are now stored in a cookie (signed and Base-64 encoded).
Form_spam_protection stores form_keys in the session.
Make sure spambots implement both cookies and javascript, by storing hashed (with salt) keys in the session.
In each session, keep only the 30 most recent :form_keys generated by form_spam_protection.
This should be more than enough for ordinary usage, but prevents the session data from
becoming inordinately large.
Also, burnt-orange rulz!
