I have been concerned that I hadn't made our ADRs for December yet... so I finally got it together and sent the hubby and sons away for the afternoon while I finished planning our itinerary for December 21st through the 30th. I checked Extra Magic Hours, and consulted the crowd levels from Unofficial Guide. Then, I made a list of all the restaurants we wanted to eat at, assuming I could get maybe half of them for ADRs.
Believe it or not, I was able to get ALL 8 of my ADRs for the days and times I wanted! Even a dinner at Le Cellier at 6:40 the night after Christmas

Many of my ADRs were for 6 or 7 people (various people coming to visit). I was shocked that they were all available! Some of the other popular restaurants on our list include O'hana (yummy!), Artist Point (Salmon!), Boma (Zebra Domes!), Biergarten (Beer!), Liberty Tree Tavern (Pot Roast!), and Rose and Crown (Illuminations!)
So, if you haven't made ADRs for December yet, get on with it while there is still availability!