I do it when I'm at school for just one class. There isn't a stereo to steal and I don't leave anything in the car. Plus I have a fuel cutoff switch that I can guarantee nobody will find so I know the car won't go anywhere.

Besides, its really easy to get into a convertible if they want to steal something out of it. You could probably cut through a top with a pocket knife, stick your hand in, and unlock the door.