Photoshop Tennis

To start a match, one player "serves" a Photoshop image to the other. The opponent takes the image, adds a new element to create a whole new picture and returns it to the serving player. For example, the houses of parliament could be sent to the USA, given a new paint job, and then be sent back for more tweaking. The rally carries on as each player adds to the image, until the match ends. This is decided by either a time limit, a forfeit or by mutual consent. Spectators can add comments in real time and then vote for a winner.
It's not exactly Wimbledon, but it's a good way to find design buddies online.