I've been investigating why certain major shopping and price comparison sites dominate the search results for "review"-related phrases even when they don't carry reviews, and I discovered that on many of them, Google is indexing the text of the Adsense ads they carry on their pages. This seems absurd to me.
I tested my theory by putting a unique phrase in an AdWords ad of mine which was appearing on these sites, and sure enough, the sites quickly went to the top of the organic results for that phrase.
I can see why it happens: the sites concerned are all big enough to be allowed to run their Adsense ads in their own styles, so the text of the ads does appear in the HTML, unlike standard Adsense presentation. But it does seem nonsensical.
[edited by: tedster at 4:44 pm (utc) on Jan. 9, 2008]
Yes, they certainly do and it's very irritating. I think most of the time Google gets those from MFA sites, parked pages, and premium publisher pages and indexes them due to the ads being setup different on those. We actually had problems with some of the URLs we have setup just for ads actually replace the real URL so then we had to make sure we 301'd them from the registrar. Then Google was indexing their ad URLs like www.example.com?gclid, sheesh, you pay them for ads and they screw up your site and give duplicate content issues. VERY irritating indeed. You would think Google would be smarter than this...