All realms will be down for maintenance tomorrow, February 10th, from 3:00 a.m. PST / 6:00 a.m. EST until 11:00 a.m. PST / 2:00 p.m. EST.
The maintenance is coming about to release patch 3.0.9, which will contain a few modifications you can read about here.
There is also a good chance the PTR for patch 3.1 will be released soon. Check out WoW Insider's Guide to Patch 3.1 for more information.
If there are any problems with the patch or maintenance becomes extended, we'll let you know right away.