We were there last year (2013) November 1-6. We went to MK on November 4 and November 6. On the fourth there were no Christmas decorations, on the sixth, everything was up! We even saw what looked like a mistaken lighting of Cinderella's Dream Lights just before Wishes, for about 30 seconds. Looked like they turned them on and then realized, "Oops! These aren't supposed to go on for another two days!" but it was nice to see them even for that brief moment.
Resorts are another story I think, I believe they take longer to get their holiday decorations up.
ETA: Except the tree, the Christmas tree was not up. But wreaths, lights, window displays, etc., were all up.