I pulled out of my driveway this morning, and managed to get to the first stop-light (only about 30-40 yards), when realized that I wasn't hearing any music. So I looked down at the Empeg, to make sure that it wasn't off from when I last had it in the dock, and saw not an Empeg, but the yawning maw of an empty sled. Just as I saw that, the light turned green, so I verrrrry slowly drove over to the side of the road, got out of the truck, and got the Empeg off the roof, where I moronically left it (on the very edge, no less) while putting the rest of my stuff in the truck.
Fortunately, I don't wash my truck very often, and it's covered in a layer of black, gritty smog residue, making it difficult for anything to slide around on the metal.
Moral of the story? Don't wash and wax your car!
(And maybe don't put your player on the roof, either.)