> use an invitation code from another user. They don't have to use their real names, but if they do something fraudulent or awful both the inviter and the invitee get banned.

Interesting. Like a regular meatspace party. Gmail used it and I got the feeling of them using it as social network tracking, so I wrote it off. But this is a great application. Will have to check out Dribble if anyone will invite me on ;).