Parallax's Hidden Usefulness
Let me start by saying that this is going to be subtle, not hugely noticeable. But it is there and I haven't seen anyone mention this about ios7
The parallax effect is not just for looks. When you reach for an app, it moves the app closer to your thumb, making it easier to reach. At all the keynotes, Apple has talked about how important it is to be able to use one hand and reach everything on the screen. Well, with the iPhone 5, I always had to stretch to touch the apps in the top right corners of the springboard. With Parallax, as you reach for it, your hand naturally tilts the phone towards your thumb. This activates the parallax, which brings the app you're reaching for just a bit closer. It naturally works in whatever direction you're reaching.
It feels like the apps are magnetized to your thumb. Wherever you reach, it moves toward you. It's very smooth and not jarring.
Like I said, it is subtle, but a little bit does help. And I could easily imagine Apple making this a real feature, by making the parallax effect stronger than it currently is. In the videos, for example, the apps move much further than in the current betas. Maybe we'll see more movement in the GM.
If so, I imagine Apple could use this to introduce a larger phone, while still keeping their philosophy of being able to reach everything with one hand.