Is wearing two pairs of socks better for cold-weather backpacking?
Not necessarily. The secret to warm feet is circulation, which keeps blood flowing to your toes. If you have space in your boots, adding a second pair of socks will help; just make sure you can wiggle your toes. If your boots fit snugly, doubling your socks will limit circulation, leaving you with numb toes. If you hike a lot in winter, consider buying a pair of insulated, waterproof boots like Columbia's Titanium Ice Dragon or a moutaineering boot such as Asolo's Summit.