Actually the few weeks before and the few weeks after Thanksgiving are some of the best times to go ...........weather is nice and crowds are pretty light.....however, the week of Thanksgiving can get pretty crowded especially with alot of locals
We were at POFQ for seven days with Thanksgiving smack in the middle in '99. No problems with crowds anywhere!
Also, the weather was fantastic, with temps topping out in the high '70's with low humidity.
And I didn't have to fool around with a turkey and a house full of guests!
We almost always go for Thanksgiving week. Thursday and Friday can be pretty crowded (especially at MK and Epcot) but hte rest of the week is very light.