I live in a medium sized US city and my truck has been parked on a city street with tools in it, unlocked, for two years. Most people lock their doors here, but even in a city known for a medium amount of crime, it isn't really that bad.

Opposite anecdote: car was broken into to steal the stereo (yes its been a while ;)). The door lock was damaged and wouldn't close any longer.

A day later the car was broken into again. While the lock was still broken and no stereo in the car. Someone smashed in the side window and left the door ajar too. Nothing got stolenthat time around.

Worst part about it was that it was probably the same person breaking in both times.

Yep, they saw something last time they wanted and didnt get it.

The one time I had my car broken into was in a nice quiet town with low crime. But I was on a not-so-great street. Crime is pretty localized. Most criminals don't go very far out of their way.