One viewing and it will make you paranoid that's for sure. I have caught it here and there. I am never surprised when people leave doors open. They just get to cocky that it will never happen to them. I lived with two roommates in college that never ever thought to deadbolt the door of our apartment. Used to drive me nuts as the door lock was flimsy and often wouldn't close all the way. Sure enough a few months into living together, we were victims of a grab and go. Only a few things taken, most of it, ironicaly belonging to the two girls that never locked the door.
Not until it happens to you, do you ever realize just how easy it is to do.