Breaking news from the service status forums:
All realms will be offline until at least 6:00pm EST / 3:00pm PST. They are having to keep the realms down for this extended period due to errors in the mail system.
Essentially, every piece of mail that was sent prior to the realms going down at 8:00am EST was lost when the servers came back up. Blizzard has said that they are actively looking for a solution to the problem. We're keeping our mailbox post updated with the latest information on that front.
Hopefully this extended downtime is not foreshadowing things to come when Wrath of the Lich King starts to enter circulation tomorrow evening at midnight*.
Update: Please see this post for more information concerning the downtime.
Stay tuned to WoW Insider for more updates.
Are you ready for the challenges that await you in Northrend? WoW Insider has you covered with our 8-day guide to Preparing for Wrath. Also, check out our feature on AddOns new, old and outdated and Essential AddOns for Wrath written especially with the expansion in mind.