The biggest parts of this are the account risk, the needing to grow revenue to pay existing liabilities (which is and should be a huge warning flag for any enterprise) and just how much room there is for someone to do this better.
My only fear is that a collapse of Groupon--which I actually see as a non unrealistic possibility--will taint other Internet/tech IPOs and, even worse, prompt the Federal government into more kneejerk regulation even stupider and more onerous than Sarbanes-Oxley.