Small wikis no-doubt get the most spam. I run several smallish wikis and removing spam from them is nearly an everyday occurance. Take for instance the bomis wiki. [1]. Scroll down to the bottom and take a look at how hard it is getting hit (that's use mod)
So the idea is to build into the mediawiki software an interwiki watchlist, hosted by the foundation. This requires little modification as we can use the RSS feed that is already generated by the software and found at RC. A simple opt-in during the install of the software and a message will be sent home to retrieve the feed every so often.
What it is appropriate to do after that, i'm not sure. But there are a lot of ways it could go.
Just wanted to throw this out there and see if it has merit. I think it is a simple solution at identifying lots of spam around the web.
/Alterego
[1] http://www.bomis.com/cgi-bin/wiki.pl?RecentChanges