We've been several times in early December. This year it was 12/6 - 12/13. The "crowds" were practically non-existant. There were a few times when we encountered long lines, but we never waited in a line that had an advertised wait time of 15 minutes or more.
Yes, the most of the parks close earlier, but we found plenty to do in the evenings. Water parks were out for us - it has to be down-right HOT before I'll spend a day at the water parks, but the kids swam at the pool daily. Christmas decorations are everywhere - resorts are especially beautiful....
BUT......I've found that vacationing between Thanksgiving and Christmas can make for a whole lot of stress if I'm not way ahead of the game on my holiday shopping! I never did get my Christmas cards done this year.....oh well! A Disney trip was higher on my priority list. Perhaps they'll be New Years cards instead......