Virtual currency, once the exclusive domain of online gamers, has gone mainstream, with everyone from Facebook, American Express, Visa, and Amazon getting into the act.
In May, Amazon will launch Amazon Coins, a virtual currency for purchasing apps and in-app goods for the Kindle Fire. And then there is Bitcoin, a de-centralized digital currency distributed via open-source, peer-to-peer networks. Much like U.S. dollars were once backed by gold, Bitcoins have a limited supply and their underlying value rises and falls.
