What it is about is behavioral training. She uses her experiences training all sorts of creatures (from fish and aquatic mammals to horses, fish and humans) using only positive reinforcement. She covers the gamut of methods to stop unwanted habits (but only recommends a few of them).
By the end of the book her messages all come together in a better understanding of the use of a clicker in animal training and insights into the positive only training techniques that she endorses.
This book seems a good read for anyone, pet owner or not. Highly recommended.
(By the way, there's a newer edition of the book than the one I borrowed from my local public library.)
Don't Shoot the Dog!: The New Art of Teaching and Training