Realm Split Information and Queues In order to address player queues on highly populated realms, we're offering free character transfer moves to players on the realms listed here.
http://forums.worldofwarcraft.com/thread.html?topicId=65019653&sid=1 It's important to note that if not enough players take advantage of these free character moves, it may become necessary to split the population of a realm between two new realms, by performing the process of a Realm Split.
What is a realm split? The term realm split describes the process of taking an overpopulated realm and dividing the population between two new realms.
What will determine whether a realm will need to undergo a realm split? As severe realm overpopulation can result in unacceptable queue times for players entering the game, the need for a realm split is determined by the extent to which a realm is overpopulated. In the event of excessive overpopulation, Blizzard will examine a number of factors and explore multiple options for mitigating that overpopulation. A realm split will be executed only if Blizzard feels that the procedure represents the best option for addressing population-related issues.
Read all the notes at... World of Warcraft forums