What I've never heard is the redemption rate on those coupons. Do 100% of the buyers use them before the expiration date? Or do those count as super-awesome customers who gave up money and got nothing in return?
I've done some research on this since Groupon doesn't release the redemption statistics. 20-30% breakage (non-redemption) seems to be the estimate, but some people go as low as 10% and as high as 40% in their estimates.