9/12 Req: United States of America Federal Trade Commission, "Re: Commercial alert complaint requesting investigation of various Internet search..."

http://www.ftc.gov/os/closings/staff/commercialalertattatch.htm

Accordingly, the staff recommends that if your search engine uses paid placement, you make any changes to the presentation of your paid-ranking search results that would be necessary to clearly delineate them as such, whether they are segregated from, or inserted into, non-paid listings. Factors to be considered in making such a disclosure clear and conspicuous are prominence, placement, presentation (i.e., it uses terms and a format that are easy for consumers to understand, and that do not contradict other statements made), and proximity to a claim that it explains or qualifies.