Just read What Google Knows About You.
Out of the six suggested methods of limiting what Google knows, I am only able to protect myself with the first three. I am constantly signed in and use email regularly. To my surprise, I also seem to watch quite a number of YouTube how-to videos – and Google knows!
My question is, who exactly is the watcher? Is it like your creepy nosy neighbor? Or is it more similar to your loud mouth cousin who cannot keep any secret? The general consensus says that it is a humongous emotionless electronic brain which filters out the juicy stuff, trading these off to businesses, which will then haunt you with your own regurgitated data.
Which is it?