Lots of forums have been going down lately. Some for "security issues", others for sharing threads that are hard to control.
I know Gotham Radio's old forums was killed because people were loading worms and crap through it. I don't know how, but that's what they said.
Worst forum in the world is the Dream Theater forum. Those guys are fucking gay. I'm a big fan, but I call it like it is and it bruises their ego too easily to hear that they aren't that great anymore.