I live in Canada and shoot all winter long with temperatures down to -25C where I live and down to -60C when I get sent to the islands for work.... Have used a 60D, 5D2, and 7D in those tempertures with no problems.
#1 - spare battery in a warm place
#2 - do NOT put the camera under your coat to keep it warm, the humidity there will end your shooting.
#3 - keep your fingers warm.
#4 - if the shoulder display or rear display get cold enough to stop working, pack it in for the day.
#5 - when outside, carry the camera in a padded bag... the padding adds insulation and slows down heat loss
#6 - before you come in after a good long time in the cold, put your camera and lenses in plastic bags, seal them, and let them warm up for an hour or so inside before you take them out of the bag.... this will solve most of your condensation problems.
second most important, take lots and lots of pictures and make sure they are backed up.
most important, have fun!