Yes, of course it is.
Now is the time when non-serious buyers and sellers are off doing other things. The sellers who have their homes on the market and the buyers who are touring homes right now are the ones who are serious about moving.
Negotiations should be easier, because you both have the same goal in mind: transfer of the property. Buyers in general aren't just looking around to see if they can find a good deal. Sellers aren't just "testing the market" to see if they can get a good price.
Inspections and appraisals should be easier to schedule, because fewer people are buying and selling right now. Thus, provided that the buyer began their search with a lender's pre-approval, closings should go faster.
Sellers should consider listing in December because their homes will have less competition.
Buyers should consider finding a home in December because they'll have less competition as well.
All in all, if you're serious about buying or selling a home, don't hesitate. While others are attending Christmas and Hanukkah parties, you could be making your real estate goals come true.
Call me, and let's get started!