Pre-pay is a type of private currency in that you can restrict where people spend their money, in some cases to a single brand, outlet or service. This is good news for loyalty and also good (or bad) news for privacy depending on your point of view. For example, parents can give their children pre-paid cards with certain categories or locations locked off. However, the big news in private currencies is what’s happening in the air and in cyberspace. According to the Economist magazine, airmiles are now technically more valuable than the US dollar while over in cyberspace gamers are exchanging cyber dollars for the real thing.