This is a short but sweet update that Blizzard will be sending an additional 100,000 invites out tonight, for a total of 200,000 Mists of Pandaria invites being sent out today. Again, it will take a while for the invites to process so Blizzard recommends keeping an eye on your games list through Battle.net Account Management, as they expect invites to continue going out into the wee hours of the night and into tomorrow.

We heard you like invites so we put an invite in your invite so you can beta while you beta. -Bashiok
For more information on the invite process as a whole please refer back to today's earlier announcement: http://us.battle.net/wow/en/forum/topic/4253902117


Source:
http://us.battle.net/wow/en/forum/topic/4253902465