Never been on it. Wife has it, and if she didn't I might have one, just because it can be good for keeping in touch with more. I think she only looks in the evening, when we're relaxing in front of the tv, unwinding before bed. Honestly, I'm not sure I want to link up with past friends; we've all moved on, and while it'd be fun catching up sometime... sometimes life just moves on. Sorry, that's life.
I wish I hadn't signed up on LinkedIn, managed to wind up with two accounts. At some point I should delete them. I'm not sure what good its for, really. I get the idea about networking, but honestly I'd probably have better results networking on FB.