I just posted this question on the strategies board about 10 days ago. I got several great responses. Sorry I don't know how to link, but the post was titled "Is Thanksgiving a mistake?", or maybe do a search there for cascadecupcake. Anyway, the responses varied a bit, but most people said that if you went either BEFORE or AFTER the holiday weekend (meaning Thursday-TG, Friday, Saturday) you would be okay. The parks are very busy Thu, Fri, and Sat, and also sometimes Wed prior and the following Sun as well. Although one poster said it gets busier that entire week each year as people figure out that it is a good time to go with schools extending their holiday week a bit more now.
We will be going Thursday before Thanksgiving and leaving the Friday just after. My goal is to do all of our park visits on Friday, Sat, Sun, Mon, and Tue and be out of there for the big rush. I'm hoping that this strategy works--we are used to September when it's nice and slow!