Groupon is a great service. They can get people in the door, no doubt about it. However, before you make the final agreement, be sure you can afford the deal.
There are two types of marketing campaigns, awareness campaigns and lead campaigns.
Awareness campaigns are generally a calculated loss. You hope that customers will remember you and visit again sometime. Many businesses are realizing that a 50% discount is great for bringing customers in the door, but not so great for things like, I don't know maybe, making payroll.
A sales lead campaign, on the other hand, expects customers to buy something from the outset. More importantly, the cost of your lead is factored in so that you make a profit.
I'm not saying you shouldn't use Groupon. Just keep in mind that you may lose money in the deal today. If the deal is done right, you'll gain new customers who might not have tried your business otherwise. Whatever your loss, consider it a marketing expense.
It will pay off in the long run; but today, it comes out of your pocket.