Drawball is a site similar to Swarmsketch, but you can use any color to draw and the canvas is huge and never cleaned. Check out this awesome E.T. buried somewhere in the middle of the ball (in the extended entry). The zooming in effects on this site are really fun – reminds me of the Google Earth animation and the leveling-up in Spore.
There’s an interesting swarm story at the Wikipedia article on Drawball about a huge South Korean flag that was drawn in the middle:
In January and February 2006, a large South Korean flag was constructed on the Drawball by members of several Internet forums (or many South Korean people). The flag was constantly expanded and repaired, and as the first of many logos to come, it was quite noticeable from the ball.
Members of various communities colluded to vandalize the Korean flag. On February 27, 2006, the flag was turned almost entirely neon green. It was because of this large attack that Drawball gained its current presence. The website became so flooded that hundreds of people at a time were put in queue before being able to access the Drawball. After extensive attack, the center of the flag was eventually converted into a Pepsi logo, and, like all Drawball drawings, the space was eventually reclaimed by other users.
(thanks Rolf Steier)