After being recommended this book numerous times and reading most of it, I asked a psychologist friend what she thinks about it. Her answer was - "This book simply teaches to change your behavior in order to manipulate people for your own needs. But at the end, it's really not worth it trying to redo yourself. ... Still, it's a good idea to smile."
P.S. After embracing some of the book's ideas, if not as a personal agenda but as general knowledge, my behavior changed. I turned too aware of my conversation style, feeling boring or annoying when I talk about myself, keeping in mind the rule saying "everyone likes to talk about themselves and nobody likes to listen to others talk about themselves". The book, in fact, prevented me from behaving naturally with people I should feel at ease with.