Please see the updated information at the end of the post for the latest news.
Realms have been down today since 3:00 a.m. PDT / 6:00 a.m. EDT. A few realms were up for a short time earlier this afternoon after the maintenance was extended, however they were promptly brought back down.
There is no indication as to what problems Blizzard has encountered. While the official forums and account management are often offline right now, WoW Insider has a few sources where we are getting our information from and we'll keep you updated with the very latest.
Be glad that at least the in-game mail hasn't gone missing, and did you get that pony Ghostcrawler promised you?
Don't forget to check out WoW Insider's Guide to Patch 3.1 for all our patch information, and stay tuned throughout the evening for updates!
Update 9:30 p.m. EDT: Current announcements indicate that most realms are up and available for play, and those that are not will be available by 10:00 p.m. EDT / 7:00 p.m. PDT. Enjoy the evening!
Older updates will appear after the break.