Gartner suggests that most of the paid-for reviews won't include disclosure about the reviewer's relationship with the reviewee, which could land both parties in legal hot water. In fact, the firm expects at least two Fortune 500 companies to come under fire by the FTC for attempting to game the social system over the next two years.

"Many marketers have turned to paying for positive reviews with cash, coupons and promotions including additional hits on YouTube videos in order to pique site visitors' interests in the hope of increasing sales, customer loyalty and customer advocacy," said Gartner analyst Jenny Sussin, in a press release.

Companies are determined to generate positive buzz online, even if it means facing the FTC's wrath. Social network users develop significantly more trust in a brand when they see numerous "likes" or favorable reviews from friends, according to (PDF). That trust can translate into dollars.

Social networks are experimenting with new ways to monetize--and some of these methods are more beneficial to brands that have already enticed a large number of people to interact with the brand. For example, Facebook advertisers can buy ads that promote the company to the friends of users who have "liked" the brand, amplifying their potential reach.