I was thinking to myself the other day that Facebook does seem to serve a similar purpose to message boards, and that TBBS and the like probably wouldn't have taken off if social networks had existed ten years ago. However, I think message boards have a certain, distinct "atmosphere" that can't be replicated on those clinical blue and white sites; Facebook and Twitter. And message boards can be dedicated to narrow subjects. Facebook has groups, but they're a bit clunky to get involved in.