Does Google Adsense affect the ranking of my site

Answer: Yes, it does.

First, you site may be crawled more frequently because Google is trying to keep the Adsense ads relevant. New pages may be discovered faster.

Secondly, by placing the Adsense JavaScript on your site you are giving Google a way to collect information about your site's visitors. This includes their IP address, their browser info, referring url etc. Google can use this data to construct a more complete picture of the way your visitors use your site (bounce rate etc). This could harm you or benefit you.

By using Google Adsense ads you are also giving Google an easy way to distinguish between your ads and the rest of your content. This article explains how the location of your ads on your page may affect your ranking.