One of our LHBS here in Denver recently did a Groupon for a beginning brewers starting set. They'll probably get a lot of return business out of it, but they swore to never use Groupon again. The starter kit was 50% off, plus Groupon took another 50% from that. I guess they knew going in the Groupon itself wasn't going to be a money maker for them (just the return business), but I think they got a little overwhelmed by the amount of people that purchased it and they seemed to have a hard time keeping up with the orders.
But yes, us consumers can get some great deals from sites like Groupon