Server Maintenance on Tuesday for 10 Hours
All live Blizzard games are down for maintenance, in preparation for the StarCraft II expansion release

Post by Blizzard (Blue Tracker, Official Forum)
We will be performing scheduled game maintenance for Diablo 3 on Tuesday, March 5th. Maintenance will begin at 1:00 AM PST and is expected to last for 10 hours. During this time Diablo 3 will not be available for play. In addition, many web services may be unavailable.
Thank you for your patience.
Thank you for your patience.