By most accounts, Groupon is growing like gangbusters. It's taking market share around the world, hiring left and right, and priming for a $25 billion IPO . But how much of the group-buying site's revenues are U.S. versus international and how is it doing in its home market, especially after its disastrous Super Bowl ads ? The chart above shows a pretty good estimate of Groupon's monthly U.S. revenues based on an analysis of every Groupon deal on its site over the last year (each deal page shows how many Groupons were sold and the price). Some key takeaways: From January, 2010 to January 2011, Groupon's U.S. monthly revenues grew eightfold from $11 million to $89 million. But February saw a huge 30 percent drop-off to $62 million. Was that a backlash because of the Super Bowl ads or simply a breather after three months of crazy holiday deals?