This past fall my company sponsored a jackpot challenge on healthywage.com and I participated. We had to form teams of 5 people. Each person's entry fee was $60 but the company paid half, so it cost me $30 to enter. If your team lost 6% as a whole, you split the jackpot. My team was one of the few successful teams, and we each got $116 twelve weeks later. My only criticism was that healthywage took a healthy portion of the jackpot. My winnings should have been $163, but I only received $116 due to their fees taken off the top.
If you can count on yourself, it's a sure bet, and I say go for it! My success was a little too close for comfort due to one person on my team sucking at life, and almost ruining our team's achievement. We eeked by though. :-)