Today World of Warcraft releases the Mist of Pandaria pre-expansion patch. This version contains a large portion of the world-wide changes that we'll be seeing with Mists. If you're looking for more details about the game changes this post over on MMO-Champion has a lot of info.
Update:
Jamash in #wowuidev extracted the UI and the TOC# is 50001
Good luck today as all the addons get updated.