A simple business model that would be coherent with your current users would be let them mention what they do to loose weight, identify commercial elements (not just weight-loss powder, but also say, iTunes apps, or a organic walnut producer) to sell mentions, or better coupons to groups that pledge to follow a similar regimen. That way, you can have not only friends, but stranger who use the same technique to help y…
I really like the idea of pledging gifts... it isn't something that has come up in our brainstorms so far either. I wonder how many people would need to pledge to build up enough for something the size of a holiday? Although a much smaller gift might not provide enough of a motivation... Would the business model here to take a percentage of the pledges?
Then, when you go to eat the bowl of ice-cream or skip your workout, you think: do I really want to screw the panda bears/starving children/cancer sufferers?