You can stop Doubleclick\'s ability to track you, on and off line, HERE .
If you don\'t opt out, Doubleclick\'s ads have the ability to track you over multiple sites, and match that up with their database.
build a database profiling consumers. The database will include consumers\' names;
addresses; retail, catalog and online purchase histories; and demographic data, according
to the policy.
News.com has a few stories on this ongoing issue HERE