Shopping Gets Even More SocialBargain hunting meets viral marketing via Groupon.

Groupon transforms the art of the deal into a truly collaborative effort. The premise behind the social commerce site is simple yet ingenious: Each day,Groupon.compresents an irresistible bargain from a local retailer or restaurant, with just one catch--the offer is good only if a predetermined number of consumers take advantage within a 24-hour period. If the user minimum is met, everyone who signed up is charged for their purchase and mailed a link to print their Groupon to be redeemed; if not, the deal is canceled.

"We tell the businesses we work with, 'Make this the best deal you've ever run,'" says founder and CEO Andrew Mason. "We want consumers to feel like if it's offered on Groupon, it's the best deal available."