As of Dec 1 advertisers will no longer be able to simply show amazing results from testimonials and presenting them as typical. Under the rule from the 1980s they could exclusively show results if they added the phrase "results not typical." This is no longer the case, according to the FTC. Now, if they use such testimonials, they will also have to disclose the results that consumers can reasonably expect. In other words if a advertiser makes a success claim they have to prove it. The new rule affects all forms of advertising.

http://www.ftc.gov/opa/2009/10/endortest.shtm

There's a link on the right side for the complete rule. Warning it's 81 pages.