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Pro:
Gives gamer or competitive types motivation.
Allows users to track progress.
Provides a place to learn new routines.

Con:
Since when do gamers need motivation? Will this really motivate those fat/skinny geeks to exercise?
People can track their progress on anything including simple notebooks.
How good is the teaching part of the system going to be? Especially the free part?

One thing that concerns me is the risk of overtraining and injury. It is easy to injure yourself if you're not familiar with a new exercise. "I just need 10 points to beat Mr. X!"

OTOH, you don't want people to be too cautious either.