Regarding the grid Apple debuted as a guide for icon designers:
No icon designer I’ve asked thinks Ive’s grid is helpful. In that sense, it’s wrong. The large circle is too big. Many apps in iOS 7 use it: all the Store apps, Safari, Messages, Photos… In all these icons, the big shape in the center is simply too big.
I was intrigued by the new icons in iOS 7 because I liked the direction they were going, but I couldn’t put my finger on why they looked so weird to me. Neven explains it quite well and once I read his piece I couldn’t stop seeing how big those inner circles are on many of Apple’s icons. They look terrible.
I’m still not sure about the rounded corners on the new icons but I’m certain I’ll grow into them. However, the size of the guide’s inner circle is something that will bug me until Apple encourages designers to change or the designer community decides that Apple is wrong.