There's no official announcement yet, but Blizzard has reopened the community site forums (http://forums.worldofwarcraft.com/thread.aspx?fn=wow-general&t=7&p=1&tmp=1), and people appear to be in game.

Update: The official announcement is now on the WoW community site (http://www.worldofwarcraft.com/).

Discuss this here (http://wow.forums.thedruidsgrove.org/showthread.php?t=8129).