Social Networking sites (#21)

Laurie's sample Facebook account was very helpful to get a feel for it. I found that some universities are using it to post training events (with RSVP feature); e.g. for online search training. I wonder how many responses they get this way.
Linkedin is primarily a professional networking tool, of course. The updates I get from my Linkedin contacts include things like 'books I'm reading' and 'groups I've joined', as well as new connections and profile updates. Books read tend to be professional reading; eg. project management books and such.
New networking sites keep springing up. I got an invite for "Namyz" last week. Anyone have any experience with it? I looked at some blog posts about it thru Google and Technorati. Quite a few complaints about spamming. I decided not to accept. Some of these new sites search your contact list and automatically send invites to everyone there, without your knowledge. It pays to check before you click.