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Shortly after Facebook bought Parakey, the Web-desktop startup cofounded by star engineers Joe Hewitt and Blake Ross, Mark Zuckerberg talked about making his goof-off site the "social operating system of the Web." It was just one of a series of failed big-picture metaphors for the tongue-tied young entrepreneur. Facebook may never be an operating system. But is it such a terrible idea to make it look like one? The latest redesign is a virtual copycat of Windows.As Silicon Alley Insider's Dan Frommer first pointed out, Facebook has removed its applications dropdown menu from the top of the screen and put it down in the bottom-left corner — you know, right where Windows keeps its "Start" button. Just like Windows, alerts pop up in the lower right-hand corner of the screen. Microsoft Windows isn't deemed sexy by San Francisco's Web-designer crowd, who brag about having to launch VMware to test out Google Chrome. But, like Facebook, Microsoft has a user base in the nine digits. Zuckerberg shows he hasn't just taken Microsoft's money — he's picked up some of the software giant's mass-market, commonsense design.