I LOVE going to Disney in December! We were there Dec 2-11, 2010. The crowd levels were higher than I remember. (I have not been in Dec. for several years) If you are in the Magic Kingdom during the parade filming....it is very crowded! That first week is also Pop Warner week at the world. There were a lot of cheerleaders in the parks. We stayed at POR and some groups were staying there as well so the hotel was crowded. They were well behaved compared to some other reports I have read from people who stayed at the All Stars...
Our trip was booked before I found out we would be sharing the hotel with the cheerleaders. It turned out fine. We didn't find the crowds to be too bad in the parks. As I said, larger than I remember from years past. We still managed to get on just about every ride we wanted. Missed out on TSM...all fastpasses were gone by the time we got there. Oh well, maybe next time. MVMCP was crowded but we still had a great time. They have a set number of tickets for each party and most sell out but it is still less than a normal crowd. It is not to be missed. The Candlelight Processional is another one not to be missed. LOVE, LOVE, LOVE that show!
This year it was pretty cold in Florida when we were there. It got worse after we left. I have been many times in December and this was only the second time I have been where I needed a winter jacket. If you do go, pack for all types of weather. It can be cold but it can be warm.
Enjoy! whatever you decide.