I'm on twitter:
Haven't gotten any sales from it as far as i know, but i also try not to 'spam' my twitter with only shop updates. Then again, it's also a crazy thought people are really interested in reading what i'm doing all the time.
I do like it as a freelancer, to use twitter as sort of a substitute of the watercooler in an office. Short breaks to read up on what everyone is doing and a chitchat here and there.