LinkedIn?

Has anyone ever heard of some new site called LinkedIn? Maybe it's not new, it's just new to me. Apparently it's some professional networking site where you can make new contacts. I don't know. I've received a few invites and they were annoying me, so I signed up. However, I'm pretty much instantly regretting that decision. Likewise, I also signed up for Reunion.com, but I don't really know why.I'm pretty happy with just my Facebook profile (obviously), so I'm thinking I don't need any other sites to make me waste more time online. If anyone can think of a reason why I shouldn't delete these accounts (LinkedIn and Reunion, NOT Facebook, of course), speak now or forever hold your peace. :)