Just a couple of comments - seriously stay away from MySpace if you want to have some degree of security (or do as I do when I have to visit it - disable everything, use Firefox, and browse it on a machine on a DMZ)

For any of MySPace's functionality you need javascript or worse enabled, and allowing user content to be incorporated into pages that way is just bad!

And in terms of networking sites - I only use LinkedIn, and then mainly as a tool for keeping in touch with colleagues as they move companies. It is very unintrusive, which is nice. Dunno how many empeggers are on it - at least 2:) but feel free to look me up - Rory Alsop.