Logged-in Facebook users will also be transmitting information about their travels around the net to Facebook servers whenever they visit a page deploying the Like button, regardless of whether they actually click that button or not. Facebook also plans to transmit user data to some web services ahead of their visit — so that when you visit the site, it’s “instantly personalized.” In practice, this means that if you are new to the music site Pandora, they’ll have a custom station waiting for you based on the music you’ve liked in your profile.
While such tracking happens with third-party ad networks, they don’t know your name or anything about you other than where you go on the net. Facebook has far more to connect your browsing information to. Perhaps the closest analog is Google’s creepy Web History which tracks you around the web and records every URL you visit, but that system only works for people who install the Google Toolbar and who don’t unclick the “Web History” button when they create a Google account. That system, along with your search history, are also separate from Google’s ad tracking system, which doesn’t know your name or who your friends are.