Simply clearing cookies has never been an effective way to keep yourself anonymous online. Between HTML5's DOM storage, Flash's Local Shared Objects, Silverlight's Local Storage and new techniques like browser fingerprinting (https://panopticlick.eff.org/) there are much more effective ways for advertisers to keep track of you. Bottom line, if you don't want to be tracked/targeted by advertisers online you should be using tools like BetterPrivacy or simply using the advertiser's opt-out functionality. Some trackers like BlueKai (http://tags.bluekai.com/registry) actually offer a great deal of transparency into what they're tracking about you and allow you to control how that data is used.