My use of the tube is platy or camelbak in winter, at the resort in Tahoe mostly. Low temps around the 20's with fair wind chill some days.
I also use the blow-back-the-air into my platy, but use the locking valve off my camelbak for it so it keeps the air and water in when I crash hard - often directly on my pack, the camelbak mule, worn on the outside of my pack. And it's true, it still will freeze a little near the exposed area but unfreezes quicker. The insulated hose is a joke, because the valve freezes first. If it's bad enuf out, you can just stick the locked and air-blown valve and a bit of hose down the neck of your jacket. If it freezes, it's just a bit that you may be able to thaw in your mouth. This is only if I am surprised by conditions. If it's predicted to be a real cold day, just bring a soda bottle, like 22oz in my jacket pocket, or 2x16oz, and refill from the lodge if needed.
Some packs are copying BCA Stash packs and putting the hose into the shoulder straps, but the locked valve should go in there too. The popular camelbak zoid puts a cover over the valve instead: http://gearx.com/product_info.php?products_id=4756
I haven't had a platy break on me yet, (knocking on wood) but had a tiny hole in a camelbak resevoir. Better that than my back, and being at the resort, I know I won't die from getting wet.
There was a guy here that did a 40 below race with a sled and stuff. Montana or something, and his platy hose froze. He should have carried a simple platy cap to replace the whole hose part.
That is one advantage of platypus over camelbak.