Plenty of people would use it that wouldn't use irc though.
Personally if I'm having an off topic discussion I don't want/need any rules dictating what I can talk about, so if there was such a forum here, I wouldn't use it.
Shrapnels Bar and Grill forum I think is part of their effort to remind people that there is more here than just one game. Along with adding the side bars (remember the anger at that)
But Id have to agree with Sombre on the subject.
And also agree that IRC fills the bill. Or other forums.