I have an account with MySpace, Facebook and LinkedIn. I created the MySpace account just to reserve my name (literally nothing else is there). I created my Facebook account because a friend asked me to but I very rarely log in and do anything.

LinkedIn, however, is a very different beast that I participate in. LinkedIn is for professionals looking to keep connections to past co-workers. I've actually found positions and contracting work from LinkedIn and it's been a very helpful tool for me. I'd recommend it for any professional looking to stay connected with others. LinkedIn also keeps your full resume as your "profile" and will show anyone who has recommended you.

I like LinkedIn