Ning is cool, no doubt. Doing it all on wiki is a bit more complicated ('til you got used to it at least). The difference is: everybody can change everything on wiki, the entire architecture included. Here only the admins can. Did I see ning linked to MySpace here, which we all know is Ruppert Murdoch? I'm not sure. Oddmuse is plain and straight open source I know.
"12 minutes left to edit your comment" - are you kidding?