2009 gets the distinction of having not 3 but 4, Mercury Retrogrades. The final one for this year will begin on Dec. 27th, 2009 and go direct again on January 15, 2010.

Some other interesting December trivia:
Two full moons: Dec 2nd and Dec. 31st
Partial lunar eclipse on the 31st
Winter Solstice is on Dec 21st this year