Windows 7 is by far the “fastest selling operating system in history,” according to Microsoft. But, in case you are wondering, those Windows 7 launch parties had little to do with it (although they were fun). Most of the demand is being driven by enterprises, many of which sat out Windows Vista because of the financial crisis and, well, it sucked (no, it wasn’t the pirates’ fault). Microsoft estimates that 75 percent of enterprises are currently evaluating Windows 7. Any guesses on how fast we get to 300 million copies sold?