Please note that Blizzard betas are unoptimized "works in progress" and you will frequently encounter serious performance issues that will not be present when the game is launched. Additionally, being granted access to a beta does not guarantee that your computer will run it well, or at all. Our betas are not intended to be viewed as "game demos", but as an opportunity to peek inside the design process and help us prepare our games for launch.
MISTS OF PANDARIA BETA TECHNICAL SUPPORT
We do not provide official support for the Mists of Pandaria beta, although we do help when possible on our Mists of Pandaria Technical Support forum (Mac here) and our Beta Bug Report forum. We first recommend checking out this comprehensive support thread for possible solutions to any issues you may encounter.