I had an instance of MediaWiki running at wiki.tinyscreenfuls.com. I used it for miscellaneous things (presentations, lists, etc.) for myself, and also for Blogging Academy and the Portland Podcasting community.
The problem is, spam got to be too much of a hassle. At first, it was only a couple of vandalisms per week. I’d simply roll them back, and ban the author. But this week, the volume has increased significantly. I know I could lock down access to it, but I don’t want to mess with it right now, so I just took it down.
It will probably come back at some point, in a more secure form, but for now, it’s one less thing for me to worry about.
Want to know the ironic part? It never got that much traffic, and MediaWiki enforces the rel=nofollow tag on all links, so it wasn’t generating the spammers any Google juice. Not sure what, if anything, they were getting out of it, but they won’t be using it at all any more.