The New York Times is reporting that AOL will allow their users to opt out of tracking. This stops the behavioral information collected about visitors activities which is used to determine which ads will be presented.
AOL had a problem with their sharing of this information a couple of years ago when their aggregated information was used to find a specific user by her online activities.
Mention of a "Do Not Track" list similar to the telemarketing "Do Not Call" list could create some interesting developments as people interpret what the do not track is supposed to mean.
If ad tracking cookies become part of this then web analytics and ROI measurements will be difficult to do.