Competitive Ads and Services 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.
This does not mean that you cannot run other ad services (YPN, CJ, Linkshare, AdBrite, etc.) on your website. It simply means that those other ads cannot mimic or look like Adsense ads.
For example, many affiliate advertisers create banners (i.e. 468x60, 120x240, etc.) that look like contextual ads. These wouldn't be allowed on the same page as Google ads.
Also, placing Adbrite or YPN contextual ads on the same page as Google Adsense ads, is against the Adsense TOS.