DH and I stayed at the YC last November right around the 11th, and the tree and other decorations were already up. We also visited several other resorts and saw decorations at them as well. Things like the carousel I've heard about at the BC and the gingerbread houses and store at the GF were not up yet. We did, however get to see them making the gingerbread African village in the kitchen at AKL when we went to Boma for breakfast.
By the way, we were at WDW from January 5-11th in 2002, and decorations were still up at the parks and the resorts. While we were there we began to see them coming down.
Hope this helps-
Tracy