As a programmer that needed to improve their general 'image' skills, but will never be required to work as a graphic designer, I found this book spot-on. I can't comment on it's abilities to turn you into an professional, but as a certified novice this book definitely fulfilled my requirements.
The information is provided in a well explained and easy to follow manner, and examples are useful without being too complex. The author also manages to inject a bit of personality into the text which was pleasant and was never distracting from the matter at hand.
One feature that impressed me particularly was the ability to manage differences between GIMP versions in a concise manner. Each time the text had to diverge to discussion version differences it was easy to tell which settings or behavior
applied to me and which to ignore.
The unfortunately named "Beginning GIMP" was a much more enjoyable read than I ever would have imagined and I look forward to keep it at hand for the next time I panic at an image manipulation problem.