I'm not surprised the back button style was removed. There are plenty of developers who would misuse the style (not you guys necessarily - no offense intended) simply because they like the look of the arrows. When used inappropriately, the general purpose of the button style is lost. If absolutely necessary, any button style could be recreated without too much effort. The extra work required to do this, however, should be enough to deter developers from abusing it.
I agree with Littleodie about Core Data and Bindings. Core Data is great, but it provides much more functionality than would be necessary for most mobile applications. The big message from Apple is that developers avoid using unnecessary resources.
UINavigationController causes interfaces to behave like linked modal dialogs, so most things can be accomplished through the viewWillAppear/viewWillDisappear/etc methods. Keeping unseen view controllers synchronized through bindings wastes resources. There are cases where synchronization is necessary, but those could be handled through KVC and KVO.
I don't necessarily agree with everything Apple has done with the SDK, but I can see some of their motivations in the changes.