I run a private extranet MediaWiki wiki which has been used on and off inside my IT consulting and contracting company, Taos, Inc. We've just replaced it with an integrated extranet website (with message-based discussion forums and document management and a bunch of other extranet functions), but I'm trying to keep active in looking for opportunities to use MW and similar tech for customer IT documentation and intranet services.
-george william herbert george.herbert@gmail.com