Groupon has 83m subscribers across 43 countries

"Groupon, a three-year-old Chicago-based start-up, is by some measures the fastest growing firm in history. It notched up revenue of $94m in 2008, its first year of business. In the first quarter of 2011, revenues were $644.7m, according to information filed with US regulators.
The company sells coupons offering discounts, taking a cut in any money the business makes. It now has 83m subscribers across 43 countries.
In a letter to potential investors, Groupon's co-founder and chief executive, Andrew Mason, warned future growth could come at the expense of profit. Last year, the company lost $450m, compared with $6.9m in 2009 and $2.2m in 2008."

Source:  The Guardian, 2nd June 2011