Somehow I knew this was coming and had a similar idea for a startup, except I'd make these ads more transactional oriented and give users who triggered the ad a cut, since after all they are promoting a product/service. And I'd limit it to n ads per user per week, otherwise you can get spammy behavior out of "friends" trying to maximize their credits--sound familiar?

Anyway, we'll see how that works out. I would honestly demand money if a brand tried to associate myself with them even if it makes sense. It's time to track and rewad word-of-mouth ads--consider them this now. It's clear Facebook and others are in a position to do this. You know that $50 billion+ valuation? Doesn't sound as crazy now, does it?

update: Reading some comments on mashable, I see a good counter to my point: why should FB pay you if they don't charge you to use their site? Fair enough, but at some point users deserve to be rewarded by brands/companies (not facebook) for their loyalty and for attracting them new customers.