On a very related note, catbird convinced me to sign up for Fitocracy, which is kinda like FourSquare for exercise, but modeled a little more like a game. You get points based on how much/what kind of exercise you do, and you level up. If anyone else is using it, or just wants to check out my profile, here it is.
Edit: Hmmm, apparently if you don't have a Fitocracy account, that just takes you to a login page. How annoying =P