I just signed up today. I've found that a number of people I know (FlyerTalkers and others) are already there. I easily found a bunch of former colleagues that I had lost track of. They had scattered to the four winds, and LinkedIn seemed like a quick and easy place to look. We'll see how many of them respond to my attempts to reconnect. I'm changing careers, so I'm not so much looking to connect with them for business reasons, though it might be nice to get a reference or two from them.