I rarely engage in shameless self promotion, but this seems like an appropriate moment. My startup, Fitocracy, is built around the notion of loosely mapping the MMORPG experience to exercise and fitness. We've been getting fairly popular with the early adopter crowd and we've even been featured in XKCD and Penny-Arcade.

You can create a private beta account using this link: http://ftcy.co/jMSLsG