Google Adsense is a great tool to monetize a site — especially if you don’t have a product/service to sell and you are not promoting affiliate products.
For those running content sites with adsense as a revenue source, however, you may find that at times you get low quality ads that really don’t reflect the quality of your site. For search engine optimization experts, we sometimes get the “submit your site to 3 million search engines” type ads.
Sebastian came up with an Adsense blacklist here and you add this list to your competitive ad filter using your Adsense control panel to block such ads from appearing on your sites.
You can also use section targeting offered by Google to improve ad relevancy further.
According to Google:
Section targeting allows you to suggest sections of your text and HTML content that you’d like us to emphasize or downplay when matching ads to your site’s content. By providing us with your suggestions, you can assist us in improving your ad targeting. We recommend that only those familiar with HTML attempt to implement section targeting.
You should also organize it using the CSS optimization techniques as mentioned in a previous post to ensure the content is as close as possible to the ads being shown.
Is there a limit to the number of sites that can be added? Yes, the limit on ad exclusion was recently set to 500 by Google as noted here.