Blizzard is experiencing some problems with the servers and are taking them down for some emergency maintenance
We are aware of the ongoing issues with Authentication. We are working diligently on resolving these issues, and we apologize for the interuption in your game play. All new information will be posted here, the general forums and as breaking news. Thank you for your patience and understanding in this matter.- Elyse (Blizzard Poster)
If the servers come back up before the usual maintenance day I'll make sure to let you know.
UPDATE: Servers seemed to be back up around 12AM PST for about three more hours of play time, as I was able to log on.
Links
World of WarCraft Forums - Official Post
