This is my first O'Reilly book in the "Cookbook" series. At first I thought this book would probably contain the code and instructions for building a couple of web applications such as a shopping cart or a blog engine. This isn't that book. Rather it provides the reader with code snippets that can be used as building blocks for all kinds of applications. If I had to describe this book in one sentence I would say it is as if the author took down all the "Hmm..., I wonder how that is done?" questions and created an answer key.
One thing I like about this book is that the authors don't waste the first few chapters trying to teach or give an overview of the language. Instead they hop right into the usage of the language that relates to real world stuff.
So here is a brief overview. The book covers PHP 5 and goes over many of the new and improved features. The first six chapters provide recipes for more basic subjects (strings, numbers, dates & times, arrays, variables, and functions. Again, this isn't an intro to PHP, that is another book such as Programming PHP from O'Reilly. This is that book you reach for once you have moved from PHP basics and are ready to build some real world stuff.
By chapter seven the authors are discussing classes and objects. I like using classes when coding in C++, so this is a good chapter for those who like OOP. The next nine chapters go over web stuff starting out with basic things like cookies, forms, and databases. Then the authors go into more advanced areas like session management, XML, automation and web services (REST, SOAP, Mail, FTP, LDAP, and DNS to name a few).
The next chapter  is on the topic of graphics. This is a cool chapter if you like to create dynamic images. Things like creating a button image on the fly, or generating charts. Graphics are great to have a knowledge of because everyone likes graphical presentation of data and this chapter can help you get there.
Chapter 18 is on security and encryption which I found rather helpful. No one wants there web application to be the link that allows data to be compromised, and this chapter deals with many of those problem areas. Chapter 19 covers localization, chapter 20 is on debugging and testing. The debugging section does a great job of getting a person setup with the tools they need to properly debug an application including creating your own exception class. This is an outstanding chapter that every programmer can appreciate since every application needs debugging.
The remaining chapters cover performance tuning, regular expressions, files, directories, command line PHP, PERL and PECL. Being a Perl guy I found it interesting to see how the authors utilized regular expressions in PHP. And the chapter on command-line PHP was outstanding; I thought the recipe for creating a PHP command shell was pretty cool.
This book is like having the answer key to most of the random questions a person comes up with when writing code. I found this book to be very useful, it will be one of those references that I keep close, and gets very little shelf time. It is a solid book. It is hard to say what parts I liked best because this is one of those books that you like and must have, but then as time goes on and you use it more and more its value grows. This is an excellent book and I would strongly recommend it the PHP users that want to move to the next level.