Because some people are so stupid that they might be misled by a blogger's endorsement of a product -- drink delicious Corona Extra beer! -- the Federal Trade Commission is cracking down:
[B]ack-scratching endorsements could become tougher under a coming set of Federal Trade Commission guidelines designed to clarify how companies can court bloggers to write about their products. This summer, the government agency is expected to issue new advertising guidelines that will require bloggers to disclose when they're writing about a sponsor's product and voicing opinions that aren't their own. The new FTC guidelines say that blog authors should disclose when they're being compensated by an advertiser to discuss a product.
Maybe some other bloggers are just going to roll over for the FTC like a bunch of wussies, but I'm not going to accept this unconstitutional infringement of my First Amendment rights. They can have my delicious Corona Extra beer when they pry it from my cold, dead fingers.