In August, 1996, my Sifu sent me home from Kung Fu practice with this book. At the time, many of the concepts seemed esoteric, or at best more applicable to the "internal" arts like Baguazhang or Taijiquan than a fighting style of Kung Fu. Since that day, however, I have re-read this book dozens of times and gained a deeper understanding of Kung Fu with each reading.
This is not a "techniques" book, but rather one that explores principles and concepts for generating power, cultivating awareness and sensitivity, and learning to ground or root for a solid foundation. The essential "Five Principles" are as applicable to Wing Chun as to any of the internal arts: Being Calm, Relaxing, Centering, Grounding, Being Whole and Total.
Within the Wing Chun Concepts coursework, you'll likely find many references to concepts and principles that Peter Ralston discusses in this book.