I've just completed the initial version of a "Combating spam" page on MediaWiki.org, which can be found at http://www.mediawiki.org/wiki/Manual:Combating_spam. I'm hoping that with the right incoming links, it will become an introduction to dealing with the issue for new wiki operators, since anti-spam measures are one of our more commonly asked questions.
I'm throwing the URL out here both to gather feedback, and to make it known to the user base at large.
Rob Church