Nearly anybody who uses the internet these days has had some interaction with Google. Whether it be their search engine, GMail, YouTube, Google+ social network, AdSense ad network, or dozens of other projects they are involved with, the odds are you've been pinged by them. But what do they think they know about you? If you are logged into your Google account then visit http://www.google.com/ads/preferences to see the profile that Google has built for you. While there you can also opt out of the ad tracking stuff.