Groupon has had success (I won't say massive b/c I can't quantify massive). The reason people are poking holes in their business viability is strictly due to their recent SEC filings for an upcoming IPO. Companies that do well on the stock exchange are those that are able to show profitability. Do some business on the exchange miss on earnings/profit margins? 100%. It is probably a 50/50 coin flip on whether or not a company is going to hit their earnings reports.
Why people are "attacking" Groupon is because of their somewhat odd use of CSOI (which is vastly different from adjusted CSOI).
To run a business that is publicly traded, you have to show that costs are in order so that you can reach probability. Groupon has had somewhat exploding costs to grow quicker than their competitors (fine by me). But using history as an indicator of profitability in the future is what has everyone in a tizzy about Groupon's business viability.