Bloggers, Facebookers, Tweeters, and others who receive compensation (cash, trade, comps, etc.) in exchange for publishing product promotions or reviews must disclose this fact, or face the wrath of the Federal Trade Commission.
This is probably something all radio stations and their advertising clients will want to be aware of as they work on integrated promotions. Now, in addition to avoiding payola, lotteries, and the like, you'll need to make sure that any favorable publicity that can be tied to compensation - whether that publicity takes the form of a DJ plug, a comment on the station's website, a blog post, or something you put up on your Facebook fan page or Twitter broadcast - is properly disclosed.
Thanks to the folks at Spokane's The Purple Turtle for bringing this to my attention. You'll find their summary and a link to the 48-page FTC document HERE.