In general, I find it really interesting to see the breadth and depth of topics covered in these type of books. For any given topic, you only get to write one chapter - which means you can't go too deep, or you risk losing the focus of the reader. However, since there is a wide mix of authors, it is quite common to wildly varying topics in them. So I find it fun to read through, and get a general feel for what people are working on out there.
You can find details about the book on Wolfgang's blog page for GPU Pro, including some sample material from some of the chapters. And of course you can find the book on Amazon if you are interested in picking up a copy.
On a personal note, this book adds to my running tally of series that I have contributed to. I have been fortunate enough to contribute to the ShaderX series, Game Programming Gems series, the GameDev.net collection, a complete text on Direct3D 11 programming, an online book for Direct3D 10 programming, several online articles here on GameDev.net, and now the GPU Pro series too. It is a great time to be involved in the realtime rendering field, and I couldn't be happier contributing to it!