For me, this book is too formulaic; it is more about "getting it right" than about awakening creative inspiration. While it is true that the abstract artist needs a good grasp of design, this is not the essence of abstract art; it is a medium for expressing intangibles visually.
If you believe a 'paint by numbers' kind of approach will give you confidence to begin, by all means start with Painting Abstracts. But if you want your abstracts to sing, I would recommend working from Mary Todd Beam's book, "Celebrate Your Creative Self." (She also has a new book coming out in March of 2009.)
For me, all the examples in "Painting Abstracts" have the same emotional temperature and use exactly the same visual metaphors. To get the idea of different visual metaphors, I would recommend looking at works by artists using other mediums, especially fibre artists and ceramic artists.
What I most find missing in this book is help with awakening inspiration: in the texture of rocks and leaves and trees for example, in different moods of water. Have you ever looked at a sunset that made you gasp? No doubt we cannot all aspire to creating the same emotional impact, but it is possible to put some of that feeling into an abtract painting.
Look further than this book if you want to do more than know how to handle your medium or how to create a pleasant design.
Postscript April 20th 2009:
It is worthwhile to read Pamela Blunt's rebuttal of my review in the comments, as well as my reply. (Incidently, I gave her a 'yes' vote, even though she completely disagrees with me.) Both our comments encapsulate the two different ways of approaching abstract art. I am sure folks are more than capable of deciding which way they want to go.