I own a small business that offers a specific service done over VOIP (nothing weird) and recently used a coupon site as marketing. We offered half off for one month of our service. The coupon company takes 30 percent of what we got from the new customers coupon purchases. We lose money on this deal, but next week the first batch will be running through their first month, and we'll see how many convert to repeat customers. So far, it's looking good. But we're offering a very niche service that many people need to try before they'll buy. I think anyone that considers this should think long and hard first, and do the math on the worst case scenario. Basically though, I'm looking at it as a form of advertising that you don't pay for unless you actually get customers.