I would still buy this book, but as usual with most books, the software can be a bit eclipsed by newer free offerings. Not sure yet how to get the sketches in the books since it appears that you have to subscribe to get them. However, it gives a very detailed description of how to download the various open source libraries to get the device working. Not got the Kinect doing anything yet though although the drivers are all loaded and the green light blinks on and off. Probably my fault rather than the Kinect or the software. I have tried all the free packages to make a 3D viewer and haven't got any of them working yet, but I will keep trying.
This is a good book that clarifies many aspects of OpenNI. It also contains some good ideas for interaction models and some good advice on general programming, if you're a beginner. If you're not, you might get bored by detailed explanations of basic programming techniques in Processing (Java). It's worth the read anyway, especially the chapters on skeleton and hand tracking. Maybe there should have been more different, but less extensively documented examples, but it's definitely worth to read this anyway. Examples on GitHub are a great help too.