[Zev]

Is there anything specific that you want to do? In some cases, there might be better books for you to be reading (like OpenGL books, if you want to make some types of games). And targeting Mac vs iOS is rather different in some ways (UIKit and AppKit have lots of little corners in which they differ).

Hillegass is basically bible for Cocoa (Mac) programming. But, its not the best way to learn Cocoa Touch (iOS) for iOS. For that, I'll second Skroob's recommendation of Craig Hockenberry's book. Also, Jeff LaMarche and David Mark's Beginning iPhone Development is rather good and I personally have a nice copy of Bill Dudney and Chris Adamson's iPhone SDK Development that I'll skim on occasion.

But, you don't need to read all three of them; they basically cover the same material in different (but equally good) ways. After you've worked your way through one of them, maybe pick up Erica Sadun's The iPhone Developer Cookbook or iPhone Cool Projects by Wolfgang Ante, Mike Ash and a bunch of other really smart people.

And at some point, move away from the path documented and write your own app!