So, I know the official answer is no. But the economic incentive for Google to rank websites that use adsense higher in the SERPS is significant, it makes me wonder. I'm thinking of moving away from adsense as I want to promote skill game websites (where people play for money) which google considers gambling and is against their TOS - but I'm afraid of hurting my traffic (which is 70% google).
There is no economic incentive for google to consistently and deliberately serve up irrelevant results. If google consistently skewed it's own results,the end result would not be increased revenue from adwords, it would be increased use of alternative search engines.
This is of course true - however things are a bit more complicated than that. The Google algorithm is far from perfect. The best results are often on the second, third or fourth pages. This is especially true for high volume search terms. By manually looking for sites that don't make it to the first page of the SERPs naturally but are both deserving to be there and also happen to be serving adsense ads Google can increase their adsense revenue as well as improve their search results. I'm not saying that they are doing this - just that I believe it would be economic for them to do so. Also, even if the overall quality of the search product would be hurt by skewing SERPs towards adsense serving sites, the improvement in the adsense product for publishers would more than make up for it. Who would use Google Adsense over YPN if it meant their traffic would be cut in half or more? Not to mention that the extra revenue can help them keep down potential competitors by spending it on marketing. Anyway this is really not what I was asking. I just wanted to know if there have been any reports of adsense serving sites doing better than non adsense serving sties on the SERPS or not.
Take note when doing natural searches to see what percentages of the top 10 run Adsense. In my experience it's low because the stronger sites generate more revenue from their own products or don't want to drive traffic away from their sites. I've turned Adsense off and on with no effects on rankings.