Amazon’s payment system just gained another method in Amazon Coins, an online currency designed to encourage Kindle Fire users to buy apps and in-app items. When the currency is launched in May, Amazon will give away tens of millions of dollars worth of free Amazon Coins before enacting the standard purchase rate of 1 US Cent per coin. While the purchase of Amazon Coins is a somewhat cumbersome process, perhaps it will make some Kindle owners feel more inclined to spend big on Farmville.