ASMo last year first week in January and it was decorated but not lavishly. I only recall decor in the lobby with a really big tree.......maybe they had already taken some things down.
Basically just the main lobby food court area is decorated. They have the Christmas tree and some wreaths. Nothing really in the resort area. Its still neat though.
We were in ASMo the first week of December in 2002. There was a large tree and I believe some large wreaths on the walls behind the check in area in the lobby. The gift shop will look festive with the large amounts of Christmas stuff for sale. We never felt a lack of Christmas spirit by staying there. They were constantly playing Disney Christmas music. It was quite cool (down in the 30s some mornings), so the hot chocolate in refillable mugs was great! And there is such a "Christmasy" feel in the parks!! Each park has a huge tree! And in the AK, we saw Goofy dressed as Santa (the pic with him was our Christmas card that year!), and Mickey, Minnie, Donald, and Daisy all in holiday safari attire. And there's MVMCP and the Osborne lights, both of which have snow falling.
We absolutely LOVED going that time of year! It's so festive and the crowds were low. But, now that DD is in school, we go in October for fall break.