Don't worry, the crowds will be nowhere near summertime crowds. We went the first week of December a couple of years ago and it was great. Even though crowds have increased over the years during that time, it is still one of the least busy times of the year to go.
I also agree with other posters that the crowd calendar on touringplans.com is a great resource if you are concerned about crowds. We've used their info to plan the dates for our last few trips and our upcoming trip, and they have been very accurate.
The resorts being booked up really does not reflect how crowded the parks will be. Alot of people are under the impression that there is a correlation between the two (and understandably so....that would seem to make sense), but it really is not a prediction of how crowded it will be.