Ask HN: Pay For Privacy...Really?

If you're a free user of prezi all your presentations are public, and in order to make them private you have to subscribe and pay. That seems like a pretty genius business model that I'm sure has been used before. But is it a feature that successfully drives people to pay? Does it open too big of feature gap that competitors can differentiate against?

Facebook's privacy is a mess as it is, and it would never (hopefully) happen, but could you imagine facebook under a "Pay for Privacy" model?