I've been consulting in process improvement for 12 years. I've worked with dozens of organisations that follow the principles of the CMM.
After reading the book once I was stumped. So I read it again and I was even more confused. The book talks a lot about the history of CMMI - the founding CMM from engineering, software development etc. but doesn't tell you anything about them specifically - what makes them different.
More importantly, it didn't discuss CMMI in any detail or how to go about using it in any practical situation.
I for one was very disappointed in the book and felt compelled to write a review about it - the first time I've done so after buying and reading 50+ books based on reader recommendations.
In short, the book is poorly organised, provides a brief history of CMM/CMMI but doesn't provide any details or practical examples of how to use it, when to use it or where to use it.