I'm wondering that too. I went ahead and just joined facebook (a friend sent me an invite), and I joined linked-in a while ago. I still don't "get" what they're for. People I don't know from work (it's a big company) keep sending me whatever it is you send on linked-in, I accept the thing-a-ma-jigs from friends and other people I know, and it's supposed to be a good thing to build up your # of contacts. But I don't know what the purpose is. My friend said it's to keep in contact with people, but I already do that with friends and other people that I know. I suppose there's less of a chance that I will lose contact with some people, and I might find someone that I lost contact with, I dunno, maybe that's about it.