Karen Kingston makes great arguments in why one should finally pick up the mess that surrounds. While her reasons for clearing clutter may be Feng Shui based, there is very little actual Feng Shui in this book which may be a disappointment for those that are seeking it. An excellent Feng Shui book I would recommend is by Terah Kathryn Collins and is titled "The Western Guide to Feng Shui Room by Room".
I would skip the chapter on clutter clearing your body, too much "quack" ideas with no nitty gritty scientific evidence. I believe there is another review here which specifically sites research which has been done to disprove the entire "bowel-cleansing" segment. Sure, fiber is good for you, but let's just leave it at that!
Overall this is a quick read. It gives many reasons to stop the pack-rat mentality, clear the clutter, and open up to new positive energy that awaits.
A great clutter book I would recommend is by Sandra Fulton. She's written many in this genre. The two I would recommend are "The Messie Motivator" and "The Messies Manual". Sandra goes into detail regarding a system for cleaning (in "The Messie Motivator") which was helpful. She also goes into more details of the psyche behind the typical clutter collector, I think many "messies" will relate.
So although Karen Kingston's book provides motivation to clear it up, there are far better books available for both Feng Shui and clutter clearing.