Hobart in December rocks...I ought to know I live here! Its really laid back with nice bushwalks etc within an hours drive, lots of history, not too hot or cold, good food and just really lovely and zen like.
There will be quite a few people around getting ready for the SYD-HBA race, Taste of Tasmania etc etc which all start after Christmas.
If you want any more info drop me and PM with what you are interested in and I'll suggest stuff.