As the others have noted, condensation is the major issue for working in the cold. Bagging the camera *BEFORE* going into a warm area is the key point, but I don't like zip-lock bags for that. When my fingers are cold I just don't get a good seal so I use the plastic grocery bags or a bread bag. The key point is that the bag is much bigger than the camera so a good twist can be put in the end and it can be folded under the camera. At least as good a seal as a zipp-lock so long as the camera isn't being moved about while it is warming up. I just put the bag in my pocket before I go out - that crumpling tends to damage a zip-lock seal.
I've only seen the LCD start acting strange at about -30F (-34C) and it worked just fine after it warmed up.