This book covers the ins and outs of development for the iPhone environment and does that well. Where I feel it really excels is where it covers the areas that immediately surround the development, the parts that aren't just "how to write the code and use the libraries".
The options that are available for structuring a project are many but sometimes choosing the simplest winds up leaving you in a straightjacket further on through development. Hockenberry finds a good balance of trying to keep things as simple as possible but not so simple that there's no flexibility. Each time I took off and did things without consulting the book I'd find myself wishing I'd taken a little more time to take on his wisdom first. For example, the discussion on how to leave space so you can work with outside designers to do the images for a project and bring those into development are great.
Where I felt the book really gave me an enormous head start was in dealing with the certificates that Apple use for signing apps when transferring them to the iOS devices and uploading to the app store. The canny and thoughtful coverage of this tar pit saved me hours of time and effort (and hair) and this aspect alone made the book absolutely invaluable.
Another topic I haven't seen covered elsewhere is tracking the sales of your application using the iTunes store and the tools there, the impact that different strategies have on the sales of the app and so on. it's all well and good to talk about how to do the coding but it's getting your app to as many people as possible which drives development. It's almost a relief to find someone shining a light here and talking about it coherently.
Once I had the hang of app development, this was a book that I kept by my side and constantly referred to.