A customer recently sent me an email to join linked in, a social networking "business" site. It seems myspace is more for music fans, facebook for college or recent graduates where linked in is more for professionals.
The differences are certainly there in the UI. For instance, in facebook, you can say if a linked friend "hooked up" with you whereas there is no option for this in linked in. I guess it still goes on, but it is not something you would publish as it has little business benefit and does not make you look very professional.
I was surprised how many IBM'ers were already on the network and thank those who have linked to me. The purpose is to find connections, so I thought I would give it a little test.
The test worked. I have managed to find one lost friend through our xhtml developer. I worked with David Wyss for a while around the QuickPlace redbook and he had seemingly vanished. I had asked a few common contacts (IBM) what happened to him but they didn't know. When I searched through linked in, it found a connection through Australia (where I was looking in Switzerland) and it came through a non-IBM source (where I looked through IBM'ers). So, it seems we were not very far from each other after all - there was always 2 degrees of separation all this time and we just didn't know.