I use social networking sites for fun, on an irregular basis, I don't give a damn about their effect on my rankings, I just do it for fun. I might get a few hits to my sites from profile links, on topic links but the main point for me is to interact without having to leave the house.

I can be working on code in one window and chatting rubbish on some forum in another, for me it's the perfect way of relaxing while I work. The serps don't enter the equation.

I wouldn't be seen dead on google or yahoo groups anyhow.

I originally learnt to hand-code using social networking sites. I think blogger is a great way for people to publish their first website because it has a good xhtml parser and costs nothing to produce. Even a homeless guy can build a site using blogger and the local library, it's real democracy.