There won't be any downtime this Tuesday according to Blizzard poster Wymdar. Uther will get a few minute restart, but everything else will keep up and running. So enjoy this extra time on maintenance Tuesday! I'm guessing this is to make up for the previous botched maintenance day that fixed instances on many servers.
We will not be conducting our usual weekly maintenance during the week of Tuesday, 9/15/09. There will be no planned downtime, and no server-wide restarts.
We will, however, be restarting Uther to address an issue with a missing boat, though downtime there should only be 3-5 minutes. Everyone else, please enjoy an uninterrupted play experience!
Click here to read the official WoW forums on the subject.