People have talked about a LW study group, but I don't know if one was formed.
Reddit is one possibility.
There is a google group for the machine learning class (which I think still has open enrolment), with about 30 members but not much activity so far.
I can't speak for anyone else in the group, but since I'm enrolled in both classes I wouldn't mind discussion related to the AI class at all! :)
Here you go: http://www.ai-class.com/
They're still working out kinks in the site, and no homework is up yet, but the initial set of lectures (really really basic "what is AI/welcome to the first day of class" type stuff is up), so if you signed up, then sign in and hopefully the site will work for you.