See What Google Knows About You

If you use any of Google's products, Google probably knows a lot about you.  While there are ways to opt out of some of Google's most invasive tracking features, use of Google's products will allow them some freedom to gather information about you.

If you want to find out what information Google knows about you, simply head to:
https://www.google.com/ads/preferences

The most interesting area was the interests category.  While many of the interests did apply to me, I have no idea why Google thinks I am interested in (to name a few):

• Air Travel (when I haven't flown on a plane in years)
• Bicycles & Accessories (I don't even own a bike)
• Hygiene & Toiletries (I guess I have some interest in this area, but I don't think I have more than the average Google user), or 
• Make-Up & Cosmetics (The only time I wore make-up was when I was in a high school play)

As a final note, the last option displays your settings for opting out of interest-based advertising.  However, clearing your cookies can change this setting.  At the very bottom is a link to install the "DoubleClick opt out extension".  This will permanently set your preference to opt out, even when you clear your cookies.