Three important brand new features in IOS 5 & XCode 4 that I've come to believe in.
1) Use ARC! Automatic reference counting is compiler based memory management. It has no negative impact on performance and you will have much fewer memory leaks. You can mix ARC with older code so you can still use your old third party libraries that have not yet been converted.
2) Use the new Exception handlers. @try, @catch, @finally. These will not impact performance. I was surprised to discover that.
3) Use the new Storyboard feature. It is said that real programmers never use the xcode interface builder (IB). I can understand why many programmers believe this, but storyboarding is a new feature that I like and I am using in Say Cheese IPhone. You can organize all you interface views onto a single storyboard. And what I really like is that you can set properties prior to switching to a new segue page and you can set a delegate for catching the round trip back. Basically, you can use any page like a subroutine. And you can visually see the entire interface of your application on your storyboard.