I just purchased my sleeping bag that I will be using to get to the top of some of these summits here in the Wasatch. When I was initially looking for a bag, I looked at a few different things:
Down or Synthetic?
Synthetic bags have their benefits but based on down's weight to warmth ratio, ability to compress down much smaller than synthetic, and the overall durability of down, I chose down.
Down Quality: All down is not created equal.
The down in your Ikea comforter comes from a young goose raised and harvested for its meat at about four months old. The goose isn't able to mature causing its down to have less hairs per feather and less of the naturally occurring oils. The better down comes from more mature geese used for breeding. Their down is harvested as they shed it each spring.
The ability to "loft" is based on the number of hairs per feather, the better a down "lofts" the warmer it is. It is warmer because it has the ability to trap more air and insulate better by keeping warmth in and cold out. Loft is determined by placing the down in a cylinder and compressing it down. When the weight is released the feathers will "loft" and again fill with air. This rating is given a number with 800 fill down being the best.
I chose the North Face Solar Flare -20 degree bag for this winter. Mont Bell also makes some great bags that are worth looking at. When buying a bag for winter excursions, go with down if you are going to be carrying it anywhere. If you take care of it, the bag will outlast you.