UDPATE: Nothing. Behind-the-scenes maintenance or prep-work for some later update. Seriously. Can't find a difference...
ORIGINAYes, the Apple Store is down. We have no idea if this is for iPad pre-order setup, for some other product update/refresh, or for behind-the-scenes maintenance.
If you have any ideas, let us know in the comments and we'll update as soon as it's back!
[Thanks to Andy for the tip!]