Gym Pact iPhone App: get paid when you go to the gym

Well now I have heard everything:  this iPhone app (which they say is available for use internationally), works like like this:

You download it, register and commit to a certain number of days per week in at particular gym. You also committ to paying/being docked a certain sum if you do not meet that committment.  The money goes into a common pool and the members who meet their target of attending get paid.  I have not downloaded it,  so I can’t judge or endorse it, but you can check it out here:

Check it out here:

And I would LOVE to hear any feedback from those who have actually tried it out.