I was there from Wed Dec 27th - Sat Dec 30th in 2006. It was very crowded. While me and my DD (6 at the time) were able to get on most rides we wanted to (by utilizing Fastpass whenever possible) the place was packed.
Because it is so busy they were directing traffic one way up and down Main Street and around the hub. Meaning when you entered the park you could only walk on Mainstreet and around the hub on your right side and you couldn't walk across the hub. This also meant if you were trying to get to Adventureland you had to walk up the right side of Main Street than walk all the way around the hub to get to the entrance.
I understood this was to help control the crowds, but at times we would just get stuck and not be able to move. It also required a bit more planning about where we wanted to go so we didn't get stuck on the opposite side of where we needed to be. Meaning if you were outside the AdventureLand entrance and wanted to go to TomorrowLand you would have to walk all the way down Main Street on the AdventureLand side than back up Main Street on the TomorrowLand side.
One neat thing that happened because of the crowds was after we saw the last showing of Fantasmic. The park was closing and they were directing people out of the park down the one side but it was so congested that they opened up the alleyway behind the Main Street buildings as well.
I hopped on this opportunity. There wasn't anything too exciting to see but they did have CM's stationed the entire walk waving to you and saying "Have a good night!". It was a very unique experience.
One other thing about the crowds is that they flow over to DTD. I had to escape the crowds one night and thought we would have dinner in DTD but every place had a long line out the door. World of Disney was packed also. There really was no escaping the crowds. We ended up back at the hotel and ordered room service (which was a treat for my DD since she had never had room service before. She said "Wow you can get food delivered to your room?" LOL)
Utilize any early entries, that was the only way we made it on to most of the Fantasy Land rides that trip. I also remember our last morning getting there right at opening and heading to New Orleans Square. All the restaurants were crowded with people trying to get breakfast. We decided to have churros for breakfast from a cart (what the heck, it's a pastry and we were on vacation). There was no one over there (I think because everyone was crowding the restaurants). We walked on Haunted Mansion, got off and rode again.
Despite the crowds it was beautiful to see it decorated for the holidays. However, if I ever go that time of year I will go after Thanksgiving and before Christmas since I have read it isn't as crowded.
