It seems Google is rolling out a new kind of advertising (behaviorally targeted). Adsense publishers have been sent a mail describing the new advertising model. Here is an excerpt of the mail:

Hi,

We’re writing to let you know about the upcoming launch of interest-based advertising, which will require you to review and make any necessary changes to your site’s privacy policies. You’ll also see some new options on your Account Settings page.

Interest-based advertising will allow advertisers to show ads based on a user’s previous interactions with them, such as visits to advertiser website and also to reach users based on their interests (e.g. “sports enthusiast”).  To develop interest categories, we will recognize the types of web pages users visit throughout the Google content network.  As an example, if they visit a number of sports pages, we will add them to the “sports enthusiast” interest category.  To learn more about your associated account settings, please visit the AdSense Help Center at http://www.google.com/adsense/support/bin/topic.py?topic=20310.

As a result of this announcement, your privacy policy will now need to reflect the use of interest-based advertising. Please review the information at https://www.google.com/adsense/support/bin/answer.py?answer=100557 to ensure that your site’s privacy policies are up-to-date, and make any necessary changes by April 8, 2009.  Because publisher sites and laws vary across countries, we’re unfortunately unable to suggest specific privacy policy language.

For more information about interest-based advertising, you can also visit the Inside AdSense Blog at http://adsense.blogspot.com/2009/03/driving-monetization-with-ads-that.html.

We appreciate your participation and look forward to this upcoming enhancement.

Sincerely,

The Google AdSense Team