I registered as an iOS developer with Apple and have been building simple iOS apps for the iPhone and iPad for awhile. These aren't professional apps mind you, but apps I develop and install on my own iPhone and iPad for kicks. I've read numerous books on iOS development and recently picked up a new book as part of the O'Reilly Blogger Review Program, called Programming iOS 5 - Fundamentals of iPhone, iPad, and iPod touch Development.
Let me start by saying that Programming iOS 5 is a long, in-depth book not for the feint of heart. I knew this before selecting the book as it states it is 1016 pages and the comments reinforced the fact that it was long, but I still wasn't prepared for just how long the book felt. It was a tough read for a couple of reasons. First, I have already read numerous books that touched on many of the subjects. And, second, it is a concept book and not meant to be a cookbook that shows you how to build apps from start to finish.
Programming iOS 5 is a great reference book that you read while you're reading iOS books that teach you the basics of building iPhone and iPad apps. A beginner will get lost and bored by the detail in this book until they have actually built ( or are building ) an app and either came across a problem or had additional questions or curiosities. This book won't get you up and programming quickly and it is way too long to sit and read for an extended period of time.
Assumes You're a Beginner
The book assumes you are a beginner with lots of coverage of programming basics as well as using Xcode. If you are an experienced developer ( like myself ), you can glance through a lot of the "language" part. You don't need to dive into OOP and just need to understand the syntax of Objective-C. Same with Xcode. Most iOS Cookbooks will give you a much quicker understanding of Xcode to be productive and then you can read Programming iOS on-the-side to get a more in-depth understanding if and when necessary. Again, the information is solid, but it's just not presented in the most interesting and fun way.
Doesn't Cover All Subjects
The book doesn't discuss all subjects, leaving out rather important subjects like Core Data. I really wasn't so concerned about this as much as other reviewers, because I took the book for what it is - a reference book for more in-depth, fundamental knowledge. Again, the book isn't teaching you how to build apps like a cookbook, but rather providing more in-depth knowledge on core subjects. You'll have to purchase other books to get more specific knowledge and to get your feet wet building apps from start to finish.
In general, the coverage of Objective-C, Xcode, Cocoa, and other topics is really good. If you've read other books on iOS 5 and feel you still don't have a solid understanding, Programming iOS 5 may be what you need to fill in the gaps. If you are a beginner excited about developing an iPhone or iPad App, I wouldn't recommend this as your first book. I recommend a solid cookbook that teaches you to build an app quickly and then perhaps purchase Programming iOS 5 if and when you want to have more in-depth knowledge at a later date.