Keep in mind that the concept of Groupon not just need a group of people to tip the deal but also would need a "sustained effort" of a group of a people behind

Keep in mind that the concept of Groupon not just need a group of people to tip the deal but also would need a "sustained effort" of a group of a people behind the scenes to get the interestingness of Groupon going. If you think about it, it's not that easy of a part to find those interesting local deals and set constraints on top of it and on and on... To me, that's one reason all these clones fail miserably.