I think most people get out of facebook what you get out of the chaos cascade and maybe twitter as well. For me, FB is really nice for staying in touch with or reconnecting with people you already know, as well as the minute to minute status stuff, if you're into that. That's why I don't really fathom Twitter- it's just one narrow aspect of other fleshed-out social networking sites.
Chaos is like this weird ragtag group of people that are kind of distant to me. This is a place where I exchange ideas, pontificate about abstract ideas, commiserate about literature and computer games and other nerdy aspects of my life....just filling in the gaps of my daily life.
Then again, myspace is the grungy twin of facebook so if there's not much to be done there beside adding bands as friends, there's probably no point in facebook.
That's pretty much where I stand with regard to Facebook, Flix, yeah. My offline friends I can't drag onto Chaos are just not active online in a communal sense at all, for whatever reason.
MySpace to me is all about the music, really. It has better music players than Facebook, but if it wasn't so useful for finding new bands and singers (And keeping me up on what they are all doing), I'd have no use for it at all.
The ultimate social networking site, for me, will always be Chaos. Forums just do so much more than Facebook or MySpace ever could.