"Groupon and other group-buying services let consumers eat their cake and have it too." To me, that doesn't sound like something consumers are going to abandon very quickly. The notion that collective buying will somehow fade in the eyes of users strikes me as pretty odd - it's a flat out better way to buy, and groupon does a great job of getting worthwhile products to consumers at deep discounts.

Of the points you mention, I think Groupon's greatest worry is probably that retailers may not make the margins they'd like when using it. But even that's a difficult complaint to make work - fundamentally retailers compete with one another and Groupon is a great tool to leapfrog your competition, even if just for a temporary period.