CodeIgniter is the fastest PHP framework out there, and it works. There are very few bugs in the code. The other thing that CodeIgniter has that other frameworks don't is a good forum and excellent documentation. It has an outstanding Users Guide you can download which lists every function with a code example.
And now, there are two books out on CodeIgniter. I purchased both books, read this one from cover to cover, and am 1/3 of the way through the "Professional CodeIgniter" book, which is much slower going. I figure folks might want to know the difference before they buy.
"CodeIgniter for Rapid PHP..." is a detailed overview of CodeIgniter. First, I have to disagree with the previous reviewer. This book does not walk you through a complete application. There is part of an application in Chap 13 & 14, but that's it. This is an overview book. It is more verbose than the User's Guide, and arranges the topics in a different, perhaps, more understandable format. This is a reading book. You're not meant to sit at your computer, and input the code with this book. Instead the code is presented in a "how to do this" type of format, and now, let's move on to the next topic. There is not a consistent application throughout the book that glues all the chapters together. This could be a reference for CodeIgniter, except I wish it had a better Index. For example, there is no Model topic under M in the Index which lists only "Menu" under "M." In contrast, "Professional CodeIgniter" lists 24 subtopics under "Model" in its Index.
Having gone through the negatives, I still rate this book 4 stars, because it is very readable, and there is value to be gained from the read. It's an excellent detailed overview. There are pearls and tidbits that you pick up in the book that make it worthwhile. You get a good overall feel of CodeIgniter from the book. It's also nice to read a computer book without necessarily running to the computer every two pages. You don't need your computer to benefit from this book, unlike the "Professional CodeIgniter" book which you do need a computer, and is not as easily read which I'll review on its page.