I was introduced to this a few weeks ago.

http://layertennis.com/

Description:

We'll be playing matches using lots of different applications, from Adobe® Photoshop® to Adobe® Flash®, but the basic idea is the same no matter what tools are in use. Two artists (or two small teams of artists) will swap a file back and forth in real-time, adding to and embellishing the work. Each artist gets fifteen minutes to complete a "volley" and then we post that to the site. A third participant, a writer, provides play-by-play commentary on the action, as it happens. The matches last for ten volleys and when it's complete, everyone with an opinion sounds off in the Forums and we declare a winner.

This Week:

Aaron Draplin vs David Nakamoto
Commentary by Steven Heller

Enjoy