"Ghostery is your window into the invisible web – tags, web bugs, pixels and beacons that are included on web pages in order to get an idea of your online behavior. Ghostery tracks over 1,200 trackers and gives you a roll-call of the ad networks, behavioral data providers, web publishers, and other companies interested in your activity."
Google publishes a description of how to avoid getting tracked and then does all kind of things to get around the actions of the folks who take their advice.
