I posted this on the commuter forum for all the slush commuters, but it is good information for any winter cyclist:
On winter days when the weather is perfectly horrible, ice will build up on your brake pads. When you need your brakes (which is just about EVERY time you apply the brakes), they fail and you rocket right into danger.
On nasty, icy days, I fill a water bottle filled with household ammonia and put it in my bottle carriage (If you think you would be prone to accidently drinking it, put it somewhere else).
When my brakes start to get iced up, I squirt ammonia on them. The ammonia stays liquid at temperatures below 32 F (0 C) so it doesn't freeze. The ammonia disolves the ice.
I heard of a guy who tried this trick with alchohol, but alchohol is not good for your tires.
Naturally, you should test this method in your driveway before using it on the road just to make sure that your equipment and conditions are appropriate for this technique.