1. That's groupons business model. The average profit margin in the service industry is less than 10%. If you give people a 50% discount, you are definitely going to be losing money. The idea is that you let them try your place, then they keep coming back. In practice, most of the places I've talked to haven't seen it this way.
2. It's really expensive for what it is, and could easily tank a small businesses cash flow. I know of two different places that did $30 gift certificates for $15. Of the $15, $7.50 went to Groupon, so the businesses got $7.50 per transaction. Both sold over 1000 coupons. If half of those coupons are redeemed in the first month, and it costs $27 to service each $30 transaction, you would see a negative cash flow impact of $9,750, and a total cash flow impact of $19,500. The average restaurant spends about $850/month on advertising, so a single groupon would soak up their entire budget for two full years.
Everybody that I've talked to that has used groupon (~10 restaurants) has said that they would never use it again. It's too expensive, and the people that buy it aren't the people they want to attract.
Ultimately, I'd be surprised if somebody else didn't come in and offer the exact same service for free. It doesn't take a genius to sell stuff to people for less than it costs. Incidentally, I did a survey of some of my customers (http://barsannapolis.com) about offering the service for free, and they largely weren't interested because it doesn't produce the results they want.