We were there in 2005 for Thanksgiving. We arrived the Saturday before and left the Saturday after. Our experience was this...Saturday-Monday (Epcot and MK) not so busy. Tuesday at MGM, getting a little more crowded. Wednesday at AK...way too busy for me! MGM on Thanksgiving Day was busy, but manageable. Epcot the day after Thanksgiving, extremely crowded! We did a few rides and then spent the day touring WS.
Because of school schedules, we thought that Thanksgiving was the perfect time to go. While the parks are busy, they aren't crazy. The weather is perfect and we really enjoyed all the holiday decorations that were displayed. We are planning another trip for this year!
I think that you will really love it...
Because you are going early in the week, you will find the parks will not be very busy. Have a great trip!