My eye-opening creepy moment was after installing Facebook's android app. I had the G+ app already installed, but logged in with a dummy account which follows various people I don't know in real life. For some reason, G+ put those people in my contact list and one day I accidentally called one of them that put their phone number on G+. It never rang because I quickly hit disconnect. The next day on Facebook, guess who was suggested I add as a friend? Mystery dial.