"No central authority" ? Well, I think the guys who decide there will only be 21 million bitcoins can be considered a central authority. Currency, in any form, is deemed to have a central authority -- national currencies, for example, have real-life value because states limit the available quantity. In this case, the Bitcoins people are acting as the central bank. Especially when I see that the total produced bitcoins will be halved each year by decision.