The heavy book with the thin green cover is a "must read" book for beginning OpenCL developers. Experienced OpenCL developers could find some chapters interesting too. The book can be used both as day to day reference book and as a manual.
The detailed introduction (chapter 1) enables the reader to understand the essentially important thing - the design of the technology (OpenCL standard v.1.1). It is considered in the book from 4 sides which are reviewed in the connection with each other: platform, execution, memory and programming models. If you are the novice in OpenCL, I urgently recommend you to read introduction firstly.
The narration continues with the "Hello World" example (chapter 2). It is big enough and divided into several subsections. Each of them we can consider as simple steps to create a real OpenCL application. I like it. After 1st an 2nd chapters, I guess, it is hard enough to NOT understand how to write your own OpenCL software. Sure, in this case you need to use some reference book (or the text of OpenCL standard), but from this point you are able to do it without a special assistance.
The next several chapters represent the mentioned by me so called "reference book". In particular, chapter 3 gives a detailed account of OpenCL platform, devices and context; chapters 4 ad 5 represent in detail OpenCL C programming language (operators, types, keywords and other things which you could find in any other programming language); chapters 6, 7, 8 and 9 describe in detail remained components of the technology: kernels, memory objects, images, events and so on. Well, I've concluded that chapters from 3 to 9 could be use as a real day to day reference book. For me it is quite useful.
To tell you the truth, the chapters 10 and 11 and 13 I've skipped, because interoperability with D3D and OpenGL, and embedded development with OpenCL are not interesting for me, but for somebody it could be useful too. The chapter 12 concerns the details of the C++ wrapper API: all staff in cl.hpp header file are briefly but well described.
The second and most interesting for experienced developers part of the book describes real cases of OpenCL using. Here 9 OpenCL-implementations of the specific algorithms are well described. It looks like all of them have been taken from the real author's software. Good. Some of the algorithms are illustrated with explicative figures. I think this part of the book with case studies could be a separated book. I just want to noted that I would glad to see more case studies, especially with vectors and matrices operations.
In addition, I want to mention chapter 20 "Using OpenCL with PyOpenCL". In recent times adopting of python in high performance applications is more and more wide. There are many techniques to improve the performance of python applications, but using GPGPU in intensive computing parts of application could become real help for python developers.
Also, it could be interesting to add chapter concerning using WebCL. Sure, nowadays WebCL is not so widely used, but the next year (2012) promises to be an year of WebCL. I hope.
To sum up, what I like in this book: organization of material, good introduction in OpenCL, detailed "Hello, world" chapter, appropriate case studies, detailed "reference book" part, print quality. Dislike: too soft cover, the lack of WebCL chapter, the number of case studies could be bigger.