Hi! I'm Mehdi, a second year student of MFA Design and Technology.
I haven't read the whole iOS guideline yet but I found the following very interesting (I'm an iPhone 4 user):
- The use of colors and depth in the design of the new interfaces help a lot the easy navigation and the quality of experience with the users.
- I found the Passbook feature very useful. I never used this feature before and excited to see the wide range of abilities and functionalities combined with new creative ideas and applications in near future. I love the idea of bridging the physical world and digital barcode in simplicity of this feature.
- The overall design of the booklet itself is very user friendly, using simple font, simple explanations, using colorful texts, and using a lot of snapshots, illustrations and images help the user quickly get to the point.

 One of my favorite apps is the the YAHOO WEATHER
It's an old app but it can be a great example of designing UI for mobile apps according to the iOS guidelines.