Xbox One - It is not always online

In post show interview, Don Mattrick says box is not "always on" and teases a new game from Black Tusk studio to be revealed at E3.
— Geoff Keighley (@geoffkeighley) May 21, 2013

Great to see

UPDATE
More information confirming the always online nature of the machine.

Q:    Does Xbox One require an “always on” Internet connection?

A:    No, it does not have to be always connected, but Xbox One does require a connection to the Internet. We’re designing Xbox One to be your all-in-one entertainment system that is connected to the cloud and always ready. We are also designing it so you can play games and watch Blu-ray movies and live TV if you lose your connection.