I hate to admit this, but I leave my doors unlocked for this very reason. I drive a soft top convertible and there's always that nagging feeling that someone would rather cut my top than bother open the unlocked doors. I don't keep anything important in my car, but I figure if someone wants my baseball cap badly enough, they can have it. Just don't vandalize my car too!
We had a car stolen right out of our driveway last year! My husband (and all our mighty watch dogs) were in the house. He was between errands, no less so he could narrow down when it happened! We have a nice truck in the driveway that needs a new transmission and has a flat tire. I'm sure some dummy will get the bright idea to put fix-a-flat in the tire and think s/he can drive away in it! Of course, now the big thing is stealing the catalytic converter so we might be in a shock when we start it up!!