This book contains quite some materials from the book you can also find them in Apple's documentations. It also has quite some details on Joe Hewitt's iUI framework. But generally speaking, it lacks more detailed explanation (on CSS, AJAX, JavaScript). Here's the dilema: if you are an experienced CSS and JavaScript developer, you will find it lacking the depth. It barely scratches the surface of what real AJAX-powered iPhone applications can do. If you are somewhat a newbie developer, you will need more explanation on the subject. Unfortunately, this book falls in-between the above 2 scenarios.
After all, this is the first and only book on iPhone programming, it's a nice start for anyone that's interested.