Today (well, today if you're reading this on Wednesday, Dec. 22, 2010, which you probably are), there will be some surprise downtime in order to correct a technical issue. There's no indication of a client patch or anything like that, just some good ol' standard downtime from 8 a.m. EST / 5 a.m. PST until 2 p.m. EST / 11 a.m. PST.
If things get extended, we'll let you know about it.
The full statement by Blizzard is as follows:
Blizzard -- Maintenance
We will be performing urgent maintenance on all realms to resolve a technical issue. Maintenance will begin at 5:00 AM and conclude at approximately 11:00 AM PST.
Instead of the normal gnome doing her maintenance thing, I've included a video of some of my favorite music out there: Vince Guaraldi's O Tannenbaum, visualized to A Charlie Brown Christmas, of course.