I was excited to see this thread. My family and I will be there Jan 11-25, and it sounds like the perfect time to go. So far we have always been lucky with crowds on our trips, either we have gone during the off season, or right after Sept. 11th when no one was traveling. I don't mind that the parks won't be open as late since we will have a 20 month old, 3 year old, 4 year old, and 6 year old in our party, and they will not be able to make it late anyway.
Although, I do have to say that we went in Spetember of 2004 (I think it was) during that particularly bad hurricane season. We were there after Charlie and when Ivan was on it's way. The park was so empty that it did take away some of the magic. Sure we walked on every ride, which is great, but there is some magic when you are part of a group who are all experiencing what you are and are as excited to be there as you are.