OK, for the MyFitnessPal people as well as the general exercise nuts or wannabees:Fitocracy.com
is a not-so-perfect way to track your exercise (not weight loss) in an MMO-like social environment. You log what your exercise activity is and you gain points/XP for doing it and level up like you're a hero in an MMO. There are quests that can be done which push you to the next level of whatever you are exercising on. Most activities are there, although one famously isn't:
You can give props to people for good workouts or for completing quests, there's comments you can give for encouragement or congratulations and there are groups for all different interests, locations and other types.
They are still in beta but I can send out invitations to anyone who is interested. I've created a group called NerdNYC which you can freely join. After a while, we can begin to do group challenges that'll give us XP and let us do stuff "together". If you are interested, send me a PM with your email and I'll forward an invite to you.