DoubleClick Improved

Google will be placing an additional DoubleClick cookie on the browsers of everyone who visits a site that is part of Google’s current AdSense network. This will allow Google to serve up display ads from DoubleClick across that network of sites. It will also allow it to introduce some basic improvements such as frequency capping (letting advertisers limit how many times the same person sees the same ad), and better reporting and conversion data. All of that is great for advertisers and great for Google, which will be able to leverage its vast, existing Adsense network to push more display ads as well.
http://www.techcrunch.com/2008/08/07/googles-ad-network-now-with-double-the-cookies/

http://googleblog.blogspot.com/2008/08/new-enhancements-on-google-content.html