Despite boosting mining speed, GPUs proved less than ideal because of their power draw and resulting heat. Bitcoin miners eventually transitioned to FPGAs (Field Programmable Gate Arrays), which brought a five-fold improvement to consumption levels. By mid-2012, FPGAs lost appeal with the arrival of fully functional application-specific integrated circuit (ASIC) systems, today's standard for Bitcoin mining.

Needless to say, Bitcoin mining is now a serious endeavor and unless you're prepared to compete with professional mining operations like this guy, don't waste your time. Fortunately, however, Bitcoin's success has spawned many other virtual currencies, with nearly half a dozen deemed "major" cryptocurrencies on Wikipedia. Of those, Litecoin is among the most popular alternative to Bitcoin.