This book is a great resource for all levels of developers that utilize Jenkins. The book is not the end to end 'Bible' for Jenkins but it's a great resource that explains pretty much all the essential building blocks. It will help show you how powerful Jenkins is and how flexible it is. Once you understand how powerful and flexible Jenkins is you can easily understand that there's no way it can be covered in a book. I've read the book a couple times now and I have realized that I overlooked features for didn't fully grasp how powerful they were originally. It's also wonderful to resource to help train others team members.
What this book 'has' that you can't easily find online is an expert opinion of HOW and WHY you should setup your project with Jenkins a certain way and how you can realize commonly utilize common methodologies via Jenkins. The author has been setting up Jenkins for many year and his experience is very valuable. Personally, even after setting up half a dozen project with Jenkins I still found the book illuminating on other ways to approach Jenkins.
I personally have the Kindle version which is a great deal. I just picked up a paperback version which sits on my desk so that I can point team members to various chapters. Deployment is often a team discussion so it's great to have a resource that Artist, QA, Managers, and Devs can look at and discuss how to make better deployment flows. I utilize 2 Jenkins boxes on my current project, on that runs OSX and does Adobe product automation and iOS builds, while another Jenkins box running in Linux that does Flash builds, PHP and JavaScript Unit Tests, and deployment and build promotions. I would say 80% of what I know about Jenkins is from this book.