With the advanced features enabled, Google's free toolbar for explorer phones home with every page you surf,
and yes, it reads your cookie too. Their privacy policy confesses this, but that's only because Alexa lost a class-action lawsuit when their toolbar did the same thing, and their privacy policy failed to explain this. Worse yet, Google's toolbar updates to new versions quietly, and without asking. This means that if you have the toolbar installed, Google essentially has complete access to your hard disk every time you connect to Google (which is many times a day). Most software vendors, and even Microsoft, ask if you'd like an updated version. But not Google. Any software that updates automatically presents a massive security risk.