Social networking is huge and I'd bet that the vast majority of the people that are reading this are on at least one site. Personally I'm on two, Facebook and LinkedIn
Anyway, it's still a growing market and in case you were thinking of setting one up, TemplatePLazza have released a really nice theme that'll do the job for you.
They're also releasing a free module for Community Builder called Superthumb, a highly configurable module to display member details.
The theme works completely with Community Builder and Group Jive and looks really nice too. Click here for more information or a demo.