I prepared myself for the exam using PMBOK with this study guide (and I completed ESI's PMP Exam Prep course). Reading a chapter in PMBOK, then reading related chapter in this book, then practicing test (from ESI's PMP Exam Prep course material). It worked for me, I succeded on my first try.
This book helps to "interpret" the PMBOK. Well written, easy to read, the exam watch sections are unique. However my opinion is that the practice test questions in the book and on the companion CD are too easy.