Can't get into the App Store? Trying to update a Mac app from the Mac App Store? How about trying to get a book from the iBooks Store or music or a movie from the iTunes Store? These services have been down for quite a few hours in multiple countries, so you'll have to wait.
While the store outages are still occurring as of 11 AM ET, it appears that iCloud Mail and iCloud accounts and sign-ins are back up after a prolonged overnight outage.
We'll update this post when things are back to normal.
UPDATE: the stores are back online as of 4:10 PM ET. The issue appears to have been in DNS servers behind the scenes at Apple. We'd love to know how much that outage cost developers and Apple...