Is there any other company that knows more about individuals - their preferences, their desires, their habits, their friends, their purchases, even the documents on their computers? And is there anything preventing Google from using that information?.... Now imagine aggregating all that information on an individual, then cross-referencing it with any searches the person has done, any books they've looked at online in Google Books, any videos they've looked at in or uploaded to Google's YouTube, or any documents Google Desktop has found on their hard drive. For Google's engineers, it would be a technically trivial exercise.
You can read the whole piece on Google's Looming Privacy Threat at the site of my company, Teeming Media.