It would be up to the advertiser and if they want to cap impressions per user or not. Some advertisers simply don't care, and they'll pay to show their ad to the same person hundreds of times. Others will cap it at 3 impressions per user. YouTube/Google doesn't care, they'll show the ads for whoever is willing to pay the most.
Is this really practical for mainstream use though? If I want to buy a single bitcoin, I need to meet a stranger and bring $1,000 in cash? If this is the recommended method of acquiring bitcoins, it deserves to fail.
It's the recommended method for obtaining Bitcoin (semi) anonymously, ever since exchangers started complying with AML regulations. That, or cash-in-mail sent with a fake return address.
Facebook has to evolve from being entertainment, to being technology. For example, look at Steam. It's a platform for distributing games. It's not going away any time soon. They work to improve the platform. They're going to open the platform up, so everyone can publish games. They're not simply a website that tries to sell you games.
Facebook needs to do the same if they want to survive. They need to stop being a social networking site, and be a social networking platform, that others build from. Facebook the site, should be one site of many using that platform. I should be able to develop a social networking site built from the Facebook platform, to compete with the Facebook site. Then when my site gets old, or the Facebook site gets old, new sites emerge, and build off the data from the existing platform. This way, it lives on. However, this will never happen, and Facebook will die.
