So, I mentioned the idea of doing 404-handler caching on this list a while ago. There's a page about it on meta:

http://meta.wikipedia.org/wiki/404_handler_caching

I coded up a very simple Wiki engine that uses this technique, just to prove to myself it would work. It does, and quite nicely. The code is here for anyone who wants to take a peek:

http://wikitravel.org/~evan/wormwiki-0.1.tar.gz

I'm going to try to shoehorn this code into MediaWiki in the near future. I think it should significantly reduce load on servers.

~ESP