Nobody knows you like Google does
Two articles which help reveal just how much Google may know about you. CNNMoney's Google Knows All, Or Close Enough To Raise Concerns and InfoWorld's What search engines store about you. Below is an excerpt:
What if there were a giant database that contained your hidden insecurities, embarrassing medical questions, and the fact that you still think from time to time about your high-school girlfriend? Well, such a data store does exist -- if you've ever plugged such private topics into a search engine.
If you wish to see this for yourself, go to Google Web History. They promote this as a feature to help users track their web activity as well as identify trends in their surfing habits.