"Example 7: A college student who has earned a reputation as a video game expert maintains a personal weblog or “blog” where he posts entries about his gaming experiences. Readers of his blog frequently seek his opinions about video game hardware and software. As it has done in the past, the manufacturer of a newly released video game system sends the student a free copy of the system and asks him to write about it on his blog. He tests the new gaming system and writes a favorable review. Because his review is disseminated via a form of consumer-generated media in which his relationship to the advertiser is not inherently obvious, readers are unlikely to know that he has received the video game system free of charge in exchange for his review of the product, and given the value of the video game system, this fact likely would materially affect the credibility they attach to his endorsement. Accordingly, the blogger should clearly and conspicuously disclose that he received the gaming system free of charge. The manufacturer should advise him at the time it provides the gaming system that this connection should be disclosed, and it should have procedures in place to try to monitor his postings for compliance. "

From FTC Endorsement Guidelines http://www.ftc.gov/os/2009/10/091005revisedendorsementguides...