This book covers OpenGL Shading Language Core profile 4 and modern OpenGL usage. It does assume some familiarity with OpenGL and C++, which helps to cut down on a lot of introductory boilerplate. It's best to start reading from the beginning, as examples and recipes build on information from previous chapters and Wolff doesn't waste space repeating the same stuff over and over, which I really appreciated.
All of the examples use the newer OpenGL APIs, and there is some basic background information on how to use them. I found this useful for people like me who have been using the fixed-function API for so long. The examples also use OpenGL Mathematics (GLM), an Open Source toolkit for working with OpenGL-style vectors and matrices. I had been unaware of this toolkit, and I'll most likely be switching to it for my next project. Wolff's style is short and to the point and keeps things moving along.
The meat of the book are the recipes, covering a wide range of shading topics, including emulating the OpenGL 2.0 fixed function pipeline, image processing, soft shadows, synthetic texture generation, and particle systems. There is a lot of information here and it is well written, though it assumes the reader is not a complete novice. Be warned, this is NOT a book for beginners.
I had a couple of minor issues with the book. Most of the examples use C++ and the STL but in a few cases Wolff falls back to using malloc/free for temporary buffers. All of the recipes are based on using geometry, and even in the image processing section it is assumed we'll be processing a 3D scene. It would be nice to have some examples focused entirely on doing 2D image processing of images directly.
Those points are very minor though and in all I thought the book was exactly what I needed to bring my skills up to the most recent OpenGL and GLSL standards.
A couple of my products were accepted into the 
