Very busy Thursday through Sunday. Have been twice at Thanksgiving ,and we are going again this year. Magic Kingdom is an absolute zoo on Thanksgiving Day. We love the cooler weather and the Christmas decorations.
Like others have said, the days before Thanksgiving are no big deal. I would not want to be in MK on T-Day, though. One nice thing we experienced last November was extremely long park hours even when the crowds weren't that bad. Sorta like having the best of both worlds
I go down during thanksgiving week ALL THE TIME! It is sooo hectic until the saturday, it is soooooooooo not crowded! There are no lines compared to what they ussually are, that's because everyone's already going home
Also Thansgiving weeks cool b/c you can go to MVMCP and see all the Osbourne Christmas Lights at MGM
Also at POR they offer a GREAT Thanksgiving Turkey meal! Even the children's sized fills me up!