It’s like Facebook for adults. I use it often to check up on people I’ve heard of. Just a few minutes ago, I was looking for a colleagues business title. It was faster to look up his Linked in profile than to go ask him.
There are also a lot of affinity groups.
I’ve had several people contact me to gauge interest in new jobs through Linked In.
Facebook has pretty much been taken over by adults. Kids aren’t as high on it as they used to be.