WPMU+MediaWiki
Finally, there’s real integration of our users in Wordpress MU!
WPMU Single Sign-on lets your WPMU loggin members hop right over to MediaWiki. You really need to read up on the install instructions before you start because there are a few assumptions and a number of edits that have to be done, none the less - this opens a whole new venue to wpmu communities!
Right now, it won’t work for shared hosting. This is because there are edits required in the .htaccess and if your on shared hosting then you are almost certianly not going to have access to this.
Matthew, with CUNY, has said that there are developments taking place to lighten the weight of this problem and hopefully development will go far enough that in the future this works just wonderfully.