I drained my 12V battery overnight (the dome lights stayed on because a door was ajar). I wanted to push the car a few feet to get easier access to my battery. With the key in the "on" position and brake depressed, I couldn't shift the gear to neutral. Everything was normal after I jump started the car and drove for a bit.

It just seems like a bad thing that you can't shift out of park if you have a dead battery or similar electrical failure.