Logging in is out. So is the main WoW website. At first it was just the Argent Dawn server which our own BRK accidentally took down in the name of charity. But now it seems bigger problems are afoot. If you're in-game don't log out or try to change characters, you won't be able to get back in until these problems are resolved. If you need to change your account through the main WoW website, you also will have to wait it out.
We'll update as the situation changes.
UPDATE1: Authentication servers up. Main website still down. Resume your achievement grinding.
UPDATE2: Main website up. All clear. Come out of your bunkers. Or, uh, go back in depending on where you gaming rig lives.