Google has millions of servers world wide storing nothing but information. You as an individual have an internet trace, a few bread crumbs of information you leave behind every time you search and access information. Not to jump to any conspiracy theories but in a world of information and related information technologies, the one with the most information is also the one with the most power, and Google has petabytes worth of it :)
Well if you ever wondered what information they store about you, go manage your account and click on the dashboard setting. It will give you a summary of information that is stored and acquired for you.
Have a go at managing your account here :)