We've been using RT for several years. As one happy customer mentions at Best Practical's site, managing a project or service driven organization without RT is like watching TV without a TiVo. The software is powerful, flexible, and above all, adaptable to many styles of management for more than just technology projects. No question, the software gets 5 stars.
This book, however, is largely a reorganization of the information provided with the software. If you prefer to read printed materials instead of PDFs or HTML, this book will save you money on printer paper. But if you're looking for best practices, recipies, or enhancements such as those you'll find in the RT Wiki, you may be disappointed. In fact, for most of the advanced capabilities, you are referred by the book to other resources. The book does contain the occasional nugget, such as a half dozen lines of code to truly delete a ticket and related data. With some searching, you'd be able to find those, and better, at the RT Wiki, such as the particuarly valuable contributions from the University of Oslo (do an A9 search for "RT prosjektgruppen").
Compared to most O'Reilly books which set the bar for excellence, this one is merely average. However, I do recommend this book as an introduction for those considering whether it's worthwhile to move to RT from some other enterprise ticketing system, and for techs to give to managers who are more comfortable with hard copies than electronic documents. For any RT admin, it's certainly worthwhile to have documentation printed and organized in an easy reference, considering how much you've saved on the excellent software itself.