Most of us are using Google Adsense contextual network to generate some revenue from our websites. As for Google's explanation “Google AdSense is a fast and easy way for website publishers of all sizes to display relevant Google ads on their website's content pages and earn money”.
In general, Adsense is a complementary to Adwords and this technology delivers ads that are relevant to your site content. In general, this should enhance your visitor’s possibility to find relevant information about products and services they are looking for. Thus it is beneficial to all participants of the game. Your visitors get relevant information, Adwords advertisers get targeted traffic to their sites and Adsense publishers get paid for delivering traffic for Adwords participants.
However, you are participating in a content network publishing and this network is considered by advertisers to be less effective than the Google search network. This encourages most of advertisers to lower bids when they are using the content network. Some of them are not using the content network at all. Even worse, some of the webmasters are using the content network to drive traffic to their Made For Adsense (MFA) sites. Their goal is to trade low cost traffic from their massive Adwords campaigns into clicks from high paying words. Those sites are not delivering useful information to your visitors. Traffic from those sites is not targeted and advertisers are turning their backs to contextual advertising because of the bad quality of traffic (quality of traffic could be estimated by the amount of sales per visit).
As a webmaster using the contextual network to generate revenue from your quality content, you are interested in getting rid of low paying ads from Made for Adsense sites. The Google Adsense control panel allows you to filter sites that you don’t want to display ads from. The question is, what sites should you filter? There is a great resource that can help you: http://www.adsblacklist.com/. You can join for free and participate in their work. AdsBlackList.com is an unique project and it's purpose is to help you maximize your Adsense revenue with minimal effort. They provide you with a list of the most commonly filtered websites whose webmasters use Adwords to attract visitors for a low price click so they can convert it to a high price click on their own MFA (Made for Adsense) or Low Cost per Click site(s). I am currently trying out this service and I will share my results with you in a month. This should give us a good time sample to make a correct estimation.