Implementing a user activity log with STI. (?)

You could also try http://github.com/parolkar/pfeed

Explanation here : http://www.travisdunn.com/activity-logs-and-friend-feeds-on-rails-pfeed

This was in reply to http://groups.google.com/group/rubyonrails-talk/browse_thread/thread/3ccb0cd6684d7836?pli=1