The model is interesting but Groupon's margin will drop as more competitors come in and self-service comes in. I don't think that a 50% margin is tenable for many small businesses.

I disagree with the statement that Groupon sheds light on issues in a business. Restaurants, for example, aren't structurally built to handle that. Think about it for a second - it's really hard, even at scale to make a $10 (market price) tuna sandwich for $2.50. There are companies focused on better-serving restaurants like Corner Dish.