Had it happen to me. "F" was sitting outside garage door in the driveway, engine idling, parking brake on. I went in the house to grab my sunglasses. When I came out the car was going down the driveway -- backwards of course. Down the driveway, across the road, across the neighbor's lawn, clipping his deck, on to hit the deck on the next neighbor's house. I couldn't catch it -- almost did though. The right rear of the car hit a 4x4 post. If it had been two feet to the right, it would have gone over a 4' vertical wall. If the front wheels had swung left the car would have gone into the lake I live on. All in all, very lucky. Minimum damage to the right rear corner sheet metal, no damage to the bumper or stainless trim.
The point of the taillight took a spindle off the first neighbor's deck, didn't damage the taillight housing. Lucky there too.