I've chipped several windshields at National. Had one where the small chip turned into a crack all the way across the window within a few hours. Had another one where the rear view mirror fell of.
They've never said anything. Even had one where they circled the crack with a marker while I was returning the car, so they definately saw it. Of course, I'm sure I've just been lucky. Or maybe they cut me a break becaue I'm EE and do so much business with them.
Matt