The book seeks to give a complete overview of the Metasploit framework. This is a herculean task. They no doubt had to make hard decisions about what topics to cover as the most important. All things considered, I think they did an amazing job covering the most important facets. They start off with the basics of the framework: how it's laid out, auxiliary modules, scanners, exploits, getting shell, and what to do once you get a meterpreter session. Then we get to see some of the more advanced aspects, including writing custom fuzzers, developing exploits form scratch, and porting existing exploits into the framework. The book finishes up with a small example penetration test from start to finish. The only topic that they really seemed to skip was the Metasploit WMAP web scanning functionality. Although some Web Application topics were covered through the use of FastTrack.
The way the authours cover the subject matter is excellent. They show you each step, and call your attention to the most improtant parts along the way. It's as close as you can get to demonstration in a book, and it works very well in my opinion. They truly highlight what makes Metasploit great: it's flexibility. they show you how to modify existing modules or write your own. They show how you can use Metasploit in the actual exploit development process as well. Allowing you to birth new exploits completely in the Framework.
I have been using Metasploit since version 2, and I learned new things from this book. Whether it was small things like the SETG command, to some of the more advanced features I have never used before like msfpescan. Whether you are just starting to learn about Penetration Testing or you have been doing it from years, this book is a must read. Unless you are H.D. Moore you will be hard pressed not to get value from this book.
UPDATE: On a note of fairness, Metasploit Unleashed does cover WMAP functionality, even if it did not make it into the book.