My launcher was still the version from early November and wasn't automatically updating on launch for some reason.

To fix it I located my ffxivboot.ver file in the FFXIV install folder and changed the version manually to 2014.01.18.0000.0001 and on relaunch it properly updated to the new December version.

Before you start make a copy of ffxivboot.ver or simply rename it something like ffxivboot(bck).ver

The default location for 64bit windows is
C:\Program Files (x86)\SquareEnix\FINAL FANTASY XIV - A Realm Reborn\boot\

For 32bit windows.
C:\Program Files\SquareEnix\FINAL FANTASY XIV - A Realm Reborn\boot\

You can open and edit ffxivboot.ver with notepad but on Win7+ with default security settings you'll have to save the modified file to the desktop then drag it into the ffxiv install location and overwrite the original file.