The most frightening thing about the data Google collects is location history. It was a real wake-up when I realised they use that data to map real life social networks. They know everyone you've bumped into every day, how long you talked to them for, who you've had a one night stand with. Your daily routines, who your friends are, and more, which all can be discovered just by analysing location history.

Them knowing what your favourite coffee shop is or where you work and live is just the tip of the iceberg.

I used to be a very heavy and trusting Google user. It started to get a little bit uncomfortable when I noticed an alert on my phone notifying me that there was a restaurant nearby that I might like to try. It occurred when I had 30-40 minutes to spare, it was a restaurant that indeed looked interesting to me, and was within a 5 minute walk. Yes that's useful but my conclusion was that this company knows way too much about me. It didn't make me comfortable when Google alerted me about flights I never explicitly told it that I was taking, and offered suggestions about how to get to the Airport that suited my routine.