The strength of this book is it's brevity: 233 pp of text plus appendices. But the code samples are incomplete (fragments). You'll be able to get an idea of how pthreads work and the methods available, but you'll have a very hard time if you need to actually write code. There is an error on p.126. If you want to write code, get "Programming with POSIX Threads" by David Butenhof. It has complete code examples and is not that much longer: 305 pp of text plus appendices. But I did find this Nichols book helpful when I was curious about pthreads. I commend O'Reilly for the nice illustrations in this book -- above average. They helped convey concepts.
With all the sophisticated tools available today such as OpenMP, this book may seem quaint. However before grasping at concepts or just using tools with out any understanding or their make up it would be wise to add this to your learning curve.
This book gives a good basic understanding of Pthreads. Of course you will later have to apply it to the real world but as a learning tool this is pretty darn good. The website or path on the sight has changed since publication; but the examples are still there. Because I am using AIX it does take a little time to convert from a gcc format to an AIX format. Then a little more time to apply AIX specific advantages.
As you go from the front of the book to the end the samples get added to and new concepts become available. There are plenty of diagrams for the visual learner. I personally found the signal handling of great use.
Any way this book is not the end-all, be-all, of threads but it sure cleared a lot of concepts up for me.
As usual, O'Reilly have produced an excellent reference book. In a few respects, this book is preferable to Scott Norton's "Thread Time" - it has better examples, for one. But this book is not as detailed or complete as Norton, so I don't recommend it as the best choice on the subject.
Of the 4 I've read on the topic, this is a good book but my personal preference (based on how the information was presented, the relevance of coding examples, etc.) is for the Butenhof Pthreads book (excellent) or the Lewis, et. al. Multithreaded Programming book (also very good).