Highly recommend this product for winter shooting! I have BodyGuard CB's on my 1d series as well as my 7D to prevent the ice buildup on the back of the camera from you breath. They also do a nice job of protecting your camera from rain or wet snow. In extreme cold I stick a small chemical handwarmer in the bottom of the pouch when using my 1d series cameras to prolong battery life when shooting in -30c or colder for an extended period.
The only drawback when using this product in the cold is accessing the shutter release when you have gloves on. I cut the neoprene that covers the shutter release so that I could activate it when using gloves. If you're shooting on a tripod use a cable release or with the 7D the RC1 wireless shutter release works great.