Although I was not there at Christmas, I was there at Thanksgiving in 2011 SOLO. I had a great time! The parks are fully decorated, and everything looks great (as if they wouldn't!). I stayed at Pop Century, and did not have any issues with buses or wait times. I will admit it had been years since being at Disney, so when I was told that was a big crowd weekend, I was not sure what to expect. I did not think it was too bad. Ride lines moved fast, transportation went smoothly, it was all handled well by Disney. Do take advantage of the Extra Magic Hours! I found that not too many people did, and the morning I went to Animal Kingdom, I was able to ride Everest 10 times in a row! And I have to admit, the photograph opportunities are excellent! I got some great shots of mist coming off the water, and I was all alone on the path to take the shots!
And being there alone, you are on YOUR time schedule. I was on the go all the time, but when I got home :-( I was RELAXED.
I am headed back October 10 for another SOLO trip for 4 days and so looking forward to it!