Yes, I'm on Dribbble. There are some more here who are.
Dribbble is a social designer community where people post whatever they're working on. You can get feedback and get yourself in front of potential clients (spectators) who will contact you directly via Dribbble. It also has Twitter-like features, such as following/being followed.
There are three types of members: Spectators, prospects, and players. Spectators are people who watch community activities, usually they're potential clients who eventually contact someone whose shots they like. Prospects are people who are looking to become players. Players are those who "play", meaning people who can upload their works (shots).
It is an invitation-only community, meaning you need to get invited by someone who already is a "player". For a player to be able to invite someone, they need to have invitations. These are given out at random at any given time, so you need to watch the community closely as people who have received invitations usually offer them up on Twitter or elsewhere, sometimes even on Dribbble itself.