[Repost of a comment I made re: Google to Continue Storing Search Requests ( http://yro.slashdot.org/article.pl?sid=06/08/10/012212 )]
Google logs what you search for and any result you clicked on.
The biggest source of info for them is probably your "Google ID"/single-signon. With this info they can tie your search terms and search clickthrough info with:
* your sent and received email (Gmail)
* your schedule (Google Calendar)
* your purchases (Google Checkout)
* where you plan on going to (Google Maps / Earth)
* what you and people you know look like (Picasa Web Albums)
* news you're interested in (Google News)
* what you like watching (Google Video)
* what you like reading/talking about (Google Groups / Blogger / Notebook)
* what you talk to your friends about (Google Chat)
* every page you visit (Google Web Accelerator)
* all your website passwords, full browsing history, cookies, and bookmarks (Google Browser Sync extension for Firefox)
Google knows a whole LOT about you and I.