Hi Kat81,
We both live in the same country, maybe even the same city.
Oh yes, I have been carrying my PRS-600 in my backpack with me and (like you) been freezing my b*** off waiting for the bus or the train lately. With temperatures down to - 20 °C the reader has been quite chilled when I have picked up from my backpack to read on the bus or the train, but it has never failed. I have not seen any problems at all, on the other hand the reader has never been completely frozen either.
Keep Cool !!
ArcticBoy