I signed up for Facebook and Linkedin. I had already had a MySpace account, with nothing in it. I must say, Facebook and MySpace are very overwhelming. I can see that MySpace is popular with teenagers. I did not really care for it because there is way to much stuff on every page that I looked at. They were all too "busy". I liked Facebook for the networking aspect. So far I only have 1 friend, and she is a huge Facebook user. She has added a couple of friends and I received that notification. It is still confusing to me. I liked Linkedin. That did seem to be the more professional networking site. I contacted some of my co-workers that had already registered to ask them to be one of my contacts. We are a relatively small university, so I was surprised that there were 50 people registered from here.
I can see where privacy would be an issue on both MySpace and Facebook. I do like that both sites ask for the other person's permission before you can be added as a friend. I didn't look that in depth into Facebook, but I know on MySpace you can make your site available only to people you allow to see it. I do like that feature.
Since we are a medical school, I am not sure that either MySpace or Facebook would be useful for us. I think Linkedin would work well in communicating with the faculty.