"Apple Training Series: Mac OS X Server Essentials v. 10.6" is just what it says it is: a book on how to get Mac OS X 10.6 Server up and running, and how to configure it to support different types of environments and users. It is organized into major topics according to server services (mail services, file services, Web services, etc.), and richly illustrated with screen shots.
As the book is frequently used in classroom settings, every chapter has a classroom-style review section. But the book is not written as a textbook; you can skip around from topic to topic and use it as a "how to" guide.
The book assumes you are familiar with the concept of server services and have either a Mac OS X or Unix/Linux background. None of the topics is covered exhaustively, and some services -- the firewall, for example -- are essentially not covered at all. The emphasis is on getting Mac OS X 10.6 Server up and running quickly and supporting users.
On the whole, it is an excellent introductory volume. I would have preferred a better index, and almost every chapter could easily be expanded into a whole book. But judging the book on its intended audience and purpose, it is a winner.