Today I discovered that Google Maps knows where I work. I have never told it where I work. I searched for a location and it said something like, "5 minute commute from work!" It was right, by the way. Then I used Google to see why Google knows so much about me - apparently it guesses based on where you spend a lot of time - such as 40 hours a week - and your travel patterns. It freaked me out a bit at first.
What is the creepiest thing the internet has figured out about you?