Magic Kingdom is really busy on Christmas Day ... many people have reported that it was so full they wish they'd chosen a different park.
It will be interesting to see how this Christmas pans out - so keep your eye on the boards ..... both at New Year and Christmas the parks can fill and you can find that after about 11.00am, they are not allowing any more guests in.
Out of the four WDW parks, Epcot can absorb crowds the best ..... and if you are staying at the Beach Club or Boardwalk certainly the most convenient for you. Epcot is a great choice for New Year's Eve as you can go round World Showcase celebrating with each country as their New Year arrives - in UK that will be 7.00pm
Another alternative would be the Universal parks - I know Janice chose Universal Studios over the WDW parks for the eve of the Millennium and didn't regret it!
Disney rates will be high - December 20th - 31st is Holiday Season, the highest rate band they have.
As I say, keep a look out for trip reports and posts regarding this Christmas and New Year - last year was quite soon after Sept 11th and although they were busy, it did affect the overall attendance.