This is an excellent book. It is well written, thoughtful, and informative. I read it more than a year ago and I am still using many of the techniques I learned in it. I also often return to it to pick up a new idea or technique I did missed the first time.
Although, I still consider myself an intermediate PHP programmer after reading this book, I feel my programming has advanced meassurably thanks to the techniques I learned from it. I tend to spend more time thinking about program architecture and testing than I ever did, and I believe the code I produce is far more robust, maintainable and understandable as a result.