We had the final race at the local Cyclocross series this Sunday. It was bellow freezing, so many people did not finish the race because their cables froze up and they could not change gears anymore. One person even broke his derailleur somehow. The whole thing got caught in the chain and bent all the way back up over the cog. It was ugly looking.
I commute all year round, and I honestly can't wait for a better drive system to be available. I have to oil my chain weekly, and adjust my derailleur monthly. Already, my cables and derailleur get frozen every time I lock my bike up. I learned to park my bike in 3rd gear, so that I can pull on the cable to 1st gear when I get on my bike. This way it loosen everything, and I can shift up. If I don't, it won't shift up. I have to loosen the cables, then get off my bike and manually loosen the derailleur. Current bikes simply are not designed to be used bellow freezing. When I shop for a bike and I say I will need the bike to work in winter, I get funny looks. One sales person even went as far as saying he doubted the bike would still be under warranty if I used it in winter.
In extreme low temperatures, I even had my chain freeze. The links got stuck together, and did not rotate as they should. That's an efficient way to destroy a derailleur. I doubt in these conditions a belt would freeze too, this is why I'm not interested in belts either.
Last winter destroyed the brand new SR Suntour fork that came with my bike. The plastic bearings froze so hard they scratched the chrome off the shafts.