Update: iTunes services appear to be coming back online, though it make take some time to restore services for everybody and all devices.
Original story follows.
The iTunes Store and App Store are currently down for some people in some parts of the world, taking with it a bunch of the iTunes ecosystem. You aren't going to be downloading any movies, music, or TV shows, you won't be streaming off iTunes Radio, and your Apple TV won't even let you watch any such items. Poof, they're gone. iMessage, FaceTime, and other Apple web services don't appear to be affected.