While established brands are adopting social technologies to enhance their existing way of doing business, Groupon has the benefit of getting deals and offers around social completely.
Groupon philosophy is pretty simple: Groupon treat their customers the way Groupon like to be treated. Groupon sell stuff, which people want to buy. A great price is only half the battle - it's also got to be a great product or service. Groupon has top-rated business partners and unbeatable prices, you should feel comfortable with Groupon and trying something new - just because it's featured on Groupon. Groupon is an addiction, you can feel good about.
Groupon did this exactly with its group buying concept. It tied into the aspect of community so simplistically. If you want to get a great offer yourself, increase your chances by sharing the offer (and the brand) through your own social channels.
Groupon is absolute genius.