In fact, as someone who has resisted the characterization of Groupon as a "Ponzi scheme" on the grounds that I prefer the term actually mean something specific, this has gone a ways to explaining how that may actually be true. But the interesting scheme isn't so much in the investors, where people have been talking about it, but in the way that businesses are being paid with revenues from the subsequent Groupons, and so on. There's a lot of loan risk in a lot of directions on Groupon's balance sheet. It seems to me they don't have to be off by much for it to crumble. "Collapse" in the title is not just a linkbait word, the author really outlines how the whole thing might very quickly collapse.
I disputed this same point last week: http://news.ycombinator.com/item?id=2617760