As someone else noted the sample is very small, likely to only cover a dozen restaurants, so were talking about 6-7 places that wouldn't use it again. Also if you look at the comments made by the restaurants a lot were complaining about fraud (people photocopying groupons) and low tipping rather than lack of repeat customers (although there are a few along those lines as well).

According to the article, less than 32% of the customers visited once.

"The 32% that said they didn’t make a profit from the program reported that customers rarely bought more than the coupon deal and few returned to the business at a later date."

If over 68% of the customers returned, then I'd call that a huge success.