Currently my machines hash at a combined 42-47.5 GH/s, which would be considered underperforming. The culprit is the Single, which has been plodding away at 35-40 GH/s instead of its intended 50. I have an RMA in to Butterfly Labs for it, but I'm not holding my breath. So what do these things do?
Mining machines spend their days rapidly hashing away, building the Blockchain (the transaction log that makes Bitcoin extremely problematic to counterfeit) and validating network transactions. Once every 10 minutes, 25 Bitcoins are awarded to a miner on the network, rewarding people for their efforts. Because this is the only way Bitcoins can enter the system, and the awarding of Bitcoin for mining shuts off in 2040, there will be a maximum of 21,000,000 Bitcoin. Ever. Once 21 million Bitcoins have been distributed, mining machines earn a portion of all Bitcoin transactions, elegantly building incentive for miners to continue validating network transactions, even after the last Bitcoin has been allocated.
Bitcoin, and almost everything associated with it is like the wild west. There's a lot of theft. There's not much regulation. People love being "free" to use it as they wish, but hate that there's not much recourse if they have their coin stolen. The people making the most money aren't the ones mining, they're the ones selling the miners the equipment. New technology is rapidly outpacing the old, in an arms race of epic proportions.
But it's really interesting, and it's crazy to have watched something take off so much over the last couple of years. There's no shaking the simple fact that if you'd invested 11 dollars to buy a bitcoin a year ago, that same bitcoin would be worth $450 as of this article's creation, which is a gain of roughly 40x.