The logon announcement tells us that the process will take two hours, and each realm will be down for about 15 minutes.
Ideally this won't be something that impacts the game too long. And dang nabit, it better not, because yours truly has a lot of free time this weekend he plans to use leveling up his Shaman.
While the servers are down, why not check out WoW Insider's Guide to Patch 3.1? It'll at least keep you wowified for the time being.
And if the servers do stay down for too long this weekend, I just want to let our Editor-in-Chief Elizabeth Harper know that I'm going to join Alex in playing Warhammer.