Back in the dot–com glory days when I was working at Vindigo, some co-workers and I came up with The Great Gym Wager(tm). It was basically a contest to see who could go to the gym the mostin a 30-day span - 15 people, $20 each, winner keeps all. I think we all expected to average 3 days a week, but the three of us who won (me + Nick + Ariel, recognize) ended up going the full 30 days in a row. It was crazy cut throat.
Anyway, Alex and I kicked it off again here at dodgeball HQ. If you want to play along at home, he's got quick write-up of the rules up on The Flickr.