I used to participate in an event called the Canadian Ski Marathon, would do 2 or 3 sections per day (of 5) and a good friend of mine who did it once had to give water to a guy doing the whole thing as his bladder had leaked like that, not what you want when its really cold, getting wet that is.
I used a camel back once and had problems with the hose freezing up, even tho I had wrapped some insulation around it. It was a drag not being able to drink for awhile before getting to a checkpoint, so while some people set them up well with good insulation, Im not keen on the idea of them, would always stick to basic containers. Havent had big problems with the threads icing up, but i guess the upside down trick would work.