As a Mists of Pandaria beta tester, it is important to test the user interface and how it interacts with the game. Here are some tips for dealing with addons and the user interface during beta testing.
Start fresh. My first bit of addon advice for the beta is to start by using no addons at all. Piling on addons at the beginning defeats a lot of the purpose of seeing if the Blizzard UI itself can handle what it is being designed to do. Take a look at the UI in a bare state, see the new features with fresh eyes, and play in that mindset for your first run-through of the content. It's part of your duty, soldier.