A ComScore qSearch study shows that in March 2006, Yahoo increased the proportion of searches that contain ads with 30 percent: 59.7 percent of searches display sponsored listings. Google showed ads on 52.9 percent of searches, up 50 percent from a year ago.
Both Yahoo and Google increased the clickthrough rate for ads: Yahoo from 9.5% to 11.4%, while Google increased the clickthrough rate from 9.7% to 11.8%.
If so many people click on the ads from SERPs, does this mean they don't find relevant pages in the organic results or they click on the first link on the page, even if it's a sponsored result? I think Google shouldn't place any ad in front of the organic results, not even for commercial queries.