I use Twitter, Facebook and Linkedin and get a good deal of business and meet tons of awesome people from it.
Other General Social Network
Niche Social Networks
I Only use Twitter
I don't use social networks
I use over 10 different Social Networks
Twitter and Digg are by far the most valuable of the social networks listed in terms of seo.
Yahoo meme is a twitter clone that I don't think will take off. Bing and Google are giving twitter to much juice.
apart fro twitter, tagged is good and meme is also good looking and drives traffic....
I use facebook, twitter, digg and orkut.
I use facebook and twitter. These sites are the best.