Hi!
In 2004 we arrived at WDW on 11/27, the Sat after Thanksgiving. We didn't have park tix for that day, so we swam in the pool and later went to DTD. It was a little crowded but very manageable. Sorry, don't know how the parks were that day.
On Sunday morning, 11/28, we went to MK. I was understandably worried about the crowds and expected the worst. People were piling into MK and the security lines to get in were long. Once we got into the park and past Main St, I wondered where the crowds went. We were able to move about better than I expected for the Sunday after Thanksgiving... that is... until we got to Fantasy Land, or close to it. That's when I found out where everyone had gone. It was pretty bad.
Later in the afternoon at MK, things got a bit better crowdwise, but Fantasyland was still the hot spot. I was dying to flee Fantasy Land and go back to the resort for a break, which we did. I kept thinking tomorrow will be better. The crowds will have left.
On the Mon after Thanksgiving, we headed to MK and so did everyone else. People were piling off the monorail and the lines to get in were pretty long. I was surprised it was so darn crowded. To be honest, I felt Monday was more crowded than Sunday. Then I read most people start their vacations on Mon and end up at MK. With early December getting more and more crowded as the years progress, I'm thinking early January is the "new early December."
Have fun!
Tink