Groupon, an Internet coupon start-up that is reportedly a Google takeout target, may be the fastest growing company in history. Just two years after its launch, revenue for the Chicago-based deal network is expected to exceed $500 million in 2010, according to analysts. That tops the growth of Zynga, a social gaming company that previously held the title, which took three years to hit that mark, points out Wedbush equity analyst Lou Kerner.
