How many of Google's products and services do you use? Gmail? Google Docs? Google Checkout? Blogger.com? Chrome? Picasa? Chances are, you use a fair few Google services. Which means that Google knows a worryingly large amount about you.
To find out just how much, head to www.google.com/dashboard and log in with your normal gmail/Google account. You'll then be able to see all of the data that Google holds, all in one place. From the number of messages in your mailbox, to the most recent item you bought via Checkout, or the most recent picture you shared on Picasa.
Now, tell me honestly that you're still not worried about the IT industry's continuing relentless move to cloud computing!