I have a large collection of books on all aspects of planting, gardening techniques and design theory but this book is outstanding amongst them.
For me, the most useful part of the book are the introductory chapters which are an exposition of a subject which can be something of a black art even to the most experienced of gardeners. The author explains clearly what she means by example and underpins this with sound theory. Straight after I read this book I went out and put her ideas into practice and produced a new bed which looks superb (even in mid winter) and which I know I wont be changing as I often do. I'm currently "editing" all my other borders using the principles from this book resulting in a vast aesthetic improvement throughout my garden.
I've been gardening for over twenty years and I do it for a living and it's not often I find a book this good which elevates my knowlege base and raises the bar by so much. Money well spent, a good source book and a book which will repay re-reading.