Each of these Day One Editions will include "exclusive in-game content" unlocking unique items as well as "collectible box art". They're priced the same as standard copies, apparently.
GAME suggests these limited runs will be exclusive to them in the UK. Microsoft has not yet confirmed the existence of such a promotional campaign for their launch line-up.
Day One Edition consoles are to feature engraved controllers with 'Day One 2013' on then, as well as unlock an exclusive achievement. You can view the current list of 'Day One' titles via.