Adsense Policy Affects Publishers
Google has made several significant changes to its Adsense policies that could have a major effect on many publishers. The policy change that has stirred the most controversy in the blogosphere is to the section regarding competitive ads and services: From the Adsense Help Center:
In order to prevent user confusion, we do not permit Google ads or search boxes to be published on websites that also contain other ads or services formatted to use the same layout and colors as the Google ads or search boxes on that site. Although you may sell ads directly on your site, it is your responsibility to ensure these ads cannot be confused with Google ads.
If you are placing any non-Google ads on your site that resemble Adsense (and
there are literally hundreds) even if they are not contextually targeted ads you
may be in violation of the AdSense policies.