First things first - I'm Jewish. That being said, a few years ago, my wife and I took the kids to WDW the week after Thanksgiving. I though it was incredible what they had done (and from what I hear they do most of it overnight) to show their "Christmas spirit". In general, I believe most people _are_ in a better mood this time of year (except for flaming libs). I've got no issues with people wishing me a "Merry Christmas" because I think they're just "sharing the joy". We'll actually be in the Magic Kingdom on Christmas Day this year - I'm looking forward to it!
have a great time- and check out Stiches' Great Escape, and if you go to Epcot- (please do), check out soaring over California. Very cool.