There are a few new UI comparison pages up at the moment, comparing both iOS6 vrs 7, and Android vrs iOS
- iOS6 vrs iOS7 view comparison - very useful if you are looking to see whats changes, tho the detail is on how some of the new stuff works, eg UINavigationItem is now taller and goes under the status bar.
- iOS vrs Android comparison, which compares iOS6, 7 and Android 4.
DONT RE-SKIN EVERYTHING
While well re-skinned apps might look great and even feel like part of the platform it definitely adds a massive amount of work for bot designers and developer. It simply isn't worth it. Start your design from Holo theme and change things you need to change and leave components that work fine without changing stock.
I wonder if iOS7 is going to be similar, at least for a year or 2 while the "new UI" looks new and fresh and designers find their feet.