Hrm. I'm not sure whether "retrieving points into real cash" is a "business end of things" issue... But as soon as you do that, you're in the same space as second-life, or any number of places that have an exchange rate between site-currency and real currency. Not a bad thing, necessarily, but it comes with some issues. I'm extremely dubious about any model where the transfer of value is actually instant - I think the gamification is probably likely to lead down some bad paths.

More comments definitely unrelated to business further down in another thread.