Dabble was just pushed into full public mode, after being in a beta (does anything ever really leave beta?).
Looks like a pretty cool site - the main goal appears to be a social network growing around videos published around the internets.
It is a pretty thorough implementation, completely done in Drupal. It looks like it's pretty heavily depending on a few modules in addition to the core (namely, video, playlist, tagadelic, buddylist(?), and likely a few others). The theme looks like a complete custom job, and the only thing that tipped me off was the use of "node" in some urls. Digging deeper, I found the telltale drupal.css file on the server (but not used in the theme...)
In all, a pretty impressive application of Drupal to launch a large social network site. There are currently over 300,000 video nodes in the database, with an unknown number of users. I'll be keeping an eye on this one to see how it scales...