I was in Orlando last year the week before Christmas with my family. We went to Universal and DW. The parks were, for lack of better word, dead. The longest line I waited on was about 20 minutes and that was a couple of times. I often spent more time making my way through empty que lines than actually waiting to get on a ride. I asked a few cast members at Universal and DW and they assured me that the weeks between Thanksgiving and right before Christmas are traditionally slow. This is why we are going again this year.
As you get closer to Christmas day the crowds do increase. As we were leaving the weekend before Christmas it was obvious that the hotel was filling up. I suspect all will be well until 12/20 this year and after that all heck will break loose.