I'm a naturally frugal person, but the book helped me formulate new ways of thinking about money and my relationship with it. The major concept being that money is a representation of your life energy. You work X hours a day at an hourly rate of $Y. Knowing those numbers allows you to think about purchases in a new way. For instance, "That new phone will cost me 2.5 days of work" or "If someone offered me $500 or the new phone, which would I take?" If you chose the $500, then you know you don't need to buy the phone.
I would recommend Your Money or Your Life before all other financial "self-help" books. In fact, I think I'm going read it again.