Dr. Drang in my favourite blog post so far about iOS 7:
Most of us are better at manipulating physical objects than abstract concepts. If our software objects are given a more physical-seeming “place,” we’ll be better at using them. We see this in gestures like swiping and pinching. If the interface responds quickly enough to follow our fingers, it feels more realistic and we find it easier to use. In fact, we don’t even think about our actions; we just do them because they feel natural. I think the new depth—if handled well and consistently—will work the same way.
That in turn reminded me of my favourite essay on the future of user interfaces:
Bret Victor's A Brief Rant On The Future Of Interaction Design.
iOS 7 can't solve anything Bret talks about -- it's still very definitely Pictures Under Glass, but it does potentially open the door for a deeper spatial element coming to interface design at a platform level, and that's exciting in itself.
You can see the effect by tilting on the game's start screen.