I love this book and have recommended it to every pregnant woman I know. My husband also read most of it while I was pregnant. And we did end up with a smooth natural birth.
I found two things particularly helpful.
1. All of the birth stories in the front of the book are great for getting you into a positive state of mind about birth. They're not all perfect, blissed out births (though maybe most are), but you will walk away from reading them feeling like you CAN do this. Ask a random woman on the street about her birth experience and, unfortunately, you're probably going to hear some kind of rough story. C-section rates are wildly high in most hospitals, births are treated like medical problems, blah blah blah...so OF COURSE most stories you hear are negative. It is so important to read and hear positive stories and this book can provide them.
2. The chapter on sphincter law is something every pregnant woman should read. Ina May has put together some info there that is fascinating and makes sense on an intuitive level even before you give birth and put it into action.