I, too, have never been on Christmas Day, but have been a couple of times shortly before, and once for a day-trip between Christmas and the New Year. To fully understand my comments, you have to understand that I am a full-blown Scrooge. The Christmas season brings more stress and family disharmony than any other time I can think of (except maybe planning a wedding). That being said, I've been surprisingly pleased with my Christmas-season experiences at WDW. Nothing beats the Osborne Family Lights Spectacular. Last time I was there, it was so cold that frost killed the plants, but the "snow" drifting down on New York Street at MGM was totally believeable (and didn't accumulate as much as we had here in Michigan)! The Christmas trees at all the resorts are beautiful. We stayed at All Star Movies last time, and that one was way-cool. Be sure to make a trip to see the tree at the Wilderness Lodge; it's my perennial favorite. I've yet to see
MVMCP, but maybe we'll get to that this time. (Somehow I managed to be talked into going at the Christmas season again this year!) Last time was the first time we went to Epcot's Candlelight Processional. I wasn't too impressed, but I'm pretty sure that's just the Scrooge in me, and I would recommend that you check it out if it fits into your schedule. The Voices of Liberty sang Holiday Carols inside the American Adventure, and I just loved their accapella sound in that perfect acoustical setting.
As far as the crowds, we never had any problem. It was a little busier than when I've gone in September, but not much worse than May had been.
I'm sure you'll have a great time!
/th