The has_many_polymorphs plugin is now hosted on Rubyforge. Read about it on the brand-new official page. The new version has a bunch of performance enhancements behind the scenes.
In other news, there seems to be a proliferation of view-like (jackchristensen.com) plugins (habtm.com). I understand using views in the database itself. But I am not sure that the convenience of putting them in the ActiveRecord model outweighs the muddling of the class structure that you get. Views aren’t very DRY. Thoughts, anyone?