The book is about developing applications with CodeIgniter 1.7. It's targeted at PHP developers with enough background to know what they are doing. Although the book says that it's written for advanced developers, I would say that an intermediate programmer could probably understand it pretty well.
The book starts out with a "Getting started" chapter that tells you where to get CodeIgniter and how to install it. The author explains the MVC pattern and goes trough the framework's major features, summarily explaining each one, but without going into an in-depth description.
Chapter 2 starts by explaining what a CodeIgniter library is, and then it goes trough some of the most important ones, briefly discussing their API's and giving short examples on their usage.
For the input class, the authors point out it's XSS filters and give examples on how to use them.
I would have liked more details, and for the author to go into a more technical discussion. In an example the author used the form helper functions (form_open_multipart/form_close) without mentioning them in the text, it's not a big deal but a little annoying.
Chapter 3 moves on to the more interesting parts of CI. It explains how form validation works and extends an example from the previous chapter, after that the chapter moves on to the database, showing how to execute queries and explaining the types of result sets returned.
A big part of this chapter is dedicated to CI's Active Record layer, each method in this layer is explained and accompanied by an example.
In chapter 4 the author explains user authentication, with ample examples for everything you would need from such a system. This chapter goes into detail and it contains a lot of code, for controllers, views and models.
Chapter 5 comes as a surprise, it's about user authentication. But wait! Wasn't that chapter 4?
Well yes, while chapter 4 is all about standard methods, where you have a database, with a users table and all that stuff, this chapter is about fun things such as using oAuth and Twitter and Facebook Connect and how to use all these things in the context of CodeIgniter.
In chapter 6 the author talks about security and the features that CI provides to help you keep your code secure.
Chapter 7 is all about large scale applications, touching on subjects such as benchmarks and bottlenecks, different kinds of caching and running your application distributed across a number of machines.
Chapter 8 is another helpful chapter, it's about web services, how to do REST and XML-RPC with CodeIgniter and as with all the previous chapters, it's based on examples.
Chapter 9 is about extending CodeIgniter and it goes to list some of the more obscure features.
Like chapter 5, the final chapter (10 if you're counting), comes as a surprise. It describes how you can give back to the community, by writing a library (for example) and releasing it as open source.
So what do I think?
Well, the book is nice, it started out with a feeling of being rushed, not enough details in the first chapters, but once the author got the beginner stuff out of the way, he focused on some really cool and interesting things.
Do I recommend it?
If you want to use CodeIgniter, definitely.