Google is tweaking its infamous algorithm to bury websites littered with ads and with very little content.
The search titan is targeting those sites with layers of ads "above the fold," or at the top of the page and takes some scrolling to get to the content -- if there is any. From Google's Matt Cutts:
We understand that placing ads above-the-fold is quite common for many websites; these ads often perform well and help publishers monetize online content. This algorithmic change does not affect sites who place ads above-the-fold to a normal degree, but affects sites that go much further to load the top of the page with ads to an excessive degree or that make it hard to find the actual original content on the page.
U.S. & World
(Ironically, Danny Sullivan over at Search Engine Land reported that Google just sent him an AdSense email saying he needed more ads on his site -- but it did stress that the ads should not to be top-heavy.)
Cutts said that this will really only affect about 1 percent of searches and punish only those with static ads on the top. The pop-ups and overlays (unfortunately) won't be affected. And since Google has already started the culling, those with top-heavy ads are going to have to update their layout or be buried by the almighty Google algorithm.