Currently looking to book an early December 2015 trip myself. Looking at past info, rates are low (which usually coincides with low crowds) starting the weekend after Thanksgiving, the next week they go up a bit, then a bit more the following week, then you really start getting the Christmas crowds and the higher rates to match. I'm currently planning to be in WDW from Dec. 5th through the 15th, and I think things will remain relatively sedate during that time. Regardless, the closer you stay to Christmas the worse it will get. My last time going in December you could almost feel the crowds getting worse by the day. And of course Christmas through New Years is supposedly crazy.