Well, we here (in Indiana) have frosted three or four times since I got mine. I get it every morning, slide in a new day's CD, and they play just fine. (Today was the first frost since this thread started).
Car's in a carport with only one wall and a roof, and I'm right on water, so it get plenty of weather and inside's darned cold in the mornings. But, I have noticed no ill effects as of yet.
(off subject, the heated seats get up to tempature *fast*. I'm not even to the guardhouse in the mornings and they are feeling toasty [150 yards or so, no idle time, just starting and driving]. Great job there!)