Article in the NY Times. It reminded me the first time (and hopefully only time) that I needed to lose weight I did it as a competition with others at the office. We didn’t bet on it, but did keep track of the progress and posted it on the wall. It kept everyone motivated. Betting would certainly be a motivator for some groups.

http://www.nytimes.com/2009/02/05/health/nutrition/05fitness.html?partner=permalink&exprod=permalink