I ride all winter long. It's mostly a matter of dressing warmer and avoiding the really cold, wind-chilly days. I carry a small common-bristled paint brush that works great for whisking loose snow off my bike and really gets into the tight spots. I avoid slush and other wet stuff. Then I wipe my bike down really well after the ride and lube the chain, etc.
I suppose it doesn't really do anything extra good for my bike but neither is a lot of stuff we ride. I think it's a lot of fun to ride in winter (with the exception of the occassional ice spot
) and I figure my bike is happier being ridden than hanging in the garage.
Don't forget hydration!