Not that this is a common attack, but to add to the stew - I knew a guy who left his leather jacket in his car, which was a soft-top convertable. The jacket thief simply sliced open the top and took the jacket.

These days I just tell people to consider the inside of their car a public place, and never to leave anything in there that you wouldn't leave lying on your front fence or similar. There are simply too many ways for people to get into cars to win that game, and ultimately, few things will stop a thief who's willing to damage the car (hammer through a window, or knife through a soft-top, for example).