As I posted in an earlier thread, my parents are there now and it is insanely crowded. My dad said that the crowds on Main Street USA determined what direction you went in to the parks as the crowd from Main Street Cinema to the HUB were shoulder to shoulder and pressing against one another. They wanted to start in Adventureland, the crowd carried them to Tomorrowland.
Now, I went last year with my family. While we had a great time, I will NEVER go back for Thanksgiving. Waaay too crowded . Lines were so long that you really could only enjoy 7 or 8 rides/attractions per day. That's not value for my money and, more than anything, the crowds made it more stressful for my wife and I because we had to focus much more on our kids' safety (got trampled by some dork trying to get the "perfect picture" of Cinderella Castle by backing into the crowd entering the Magic Kingdom) due to the enormous crowds everywhere. I loved being there due to the decorations and season and all, but the crowd made the enjoyability of our trip a challenge. Never again.