I've used it as a customer but never as a business. I have unfortunately heard horror stories around here from businesses who used it although the service-based businesses (like yours) tend to fair a bit better since you're only theoretically losing your time while businesses selling product tend to lose a lot of money in merchandise.
The few things I've heard: They put a lot of pressure on businesses not to cap how many they sell so it's difficult to limit losses. They take a large chunk of the money as their fee. Customers tend to not care one bit about any of the rules associated with the Groupon so the business owner gets stuck either letting it run wild (taking coupons after they expire, taking coupons for things they weren't meant for) or having to be the bad guy since it's all on you--Groupon isn't involved any more (obviously there are some customers who are awesome and follow the rules but supposedly there are a whole lot who don't).