"what if you could alter only one pixel per day? Cameron Adams has developed Pixelfest, a collaborative effort to create "art/design/garbage" through numerous people making tiny contributions. Give it a whirl, or check out a time lapse movie of the project's development."
Try the time lapse movie playback at at a seepd of 5 or 10 (you'll see what I mean when you're there).
This experiment is similar on the co-creation Johnnie Moore and James Cherkoff did in a pub, a piece of paper, a pencil and a willing volunteer.