Groupon

We're trying our first Groupon experience tonight. I bought a $20 gift certificate to a restaurant we've been interested in trying for a while for the price of $10. So theoretically, it's a "buy one, get one free" deal, or a 50% deal. That's if we stay in the $20 range (which, btw, doesn't include tip or tax, and this particular deal doesn't include alcohol). Now if we spend an additional $10 for $30 worth of food, then we go over and our savings decrease accordingly. By then, I'll have $20 and our savings will be $10, or about 33 percent. If I spend an additional $30 on a $40 bill, then the savings decrease again. All in all, we'll see how it goes tonight. Luckily, this isn't an expensive place, so I think we'll probably spend an extra $5 or so on tax and tip. I'm just curious as to how these things work so I thought this would be a good one to try. If anyone else has tried and liked, let me know!