But that's another story. The big issue here really is convenience. You want to take a camera skiing, so I assume you want to catch photos of the resort or of your friends and family as they ski. To me, that means carrying something other than any old backpack. Not only will that put the camera out of reach, it'll be uncomfortable and awkward on chairlifts.
So, what then? Some kind of chest pack would be ideal. You might look into Lowepro's Topload Zoom 1 ($25; www.lowepro.com), which has a case style in which the camera is stuck into the bag lens-first. For another $10 you can buy a chest harness attachment. With the top-loading design, you'll then have the camera right at chest level, with easy access to the zipper. So you can have it out, shoot, and get it back in the bag in seconds. Plus, in the event of some sort of a tumble, it's already in a well-protected position. I've bruised a lot of things while skiing, but never my sternum. The Topload Zoom 1 can handle a smallish SLR like the Rebel and a short zoom lens. For a long zoom lens, go to the Topload Zoom 2 ($28).
The cold shouldn't be an issue until it gets into single digits. Generally, the camera's proximity to your body should keep it warm enough so the battery doesn't croak. As insurance, you could simply carry a spare battery in a pocket. That one will be warm and ready to go in case the one in the camera checks out for a cup of hot chocolate.
It's snowing like mad here in the Northwest. Could be quite a ski season!