For me FB and this board (or boards like this) serve two different purposes, though admittedly there is some overlap too.
FB for me is for socializing with family, current and old friends, and sharing experiences with each other, including pictures, statuses, places you're visiting etc. For instance I wouldn't have known anybody visited the Far East during some major weather issues recently, unless I were their FB friend.
Here, it's more opened ended discussion about specific topics, and these discussions last and evolve over time. I enjoy that, and being able to go back and look up old information on specific topics, whether they're jazz/music related or not. I'm not at the same place as everyone else with their musical interests and tastes, so I still feel like there's information I can learn even if it's a thread from back in 2004.
There's definitely the social aspect here too though, woven within most of the threads, and also the old (now defunct) Live Chat (Free's a dick by the way!), and there's definitely overlap between my friends here and on FB.