I first read the book more than a year ago. I've re-read it four times.
I find the principles easy to remember and sufficiently universal to help me to develop my life in the way I want to. To me, that is the best part about it - something that bowled me over the first time I read the book and delights me to this day.) Thus, I continue to use the principles regularly, at least on a weekly basis. I personally concentrate more on Truth, Love, Authority and Courage.
Because of their universality, you probably will take a long time to outgrow the principles (if ever). I started by applying them to life, then progressed to money, to career, and then to diving. In fact, as I applied the principles, my knowledge grew from head knowledge to include heart knowledge and then experential knowledge. Knowing the principles also simplifies the process of helping others - because you can relate to other people's problems without needing to have such a similar experience.
One question I have mulled about the principles are - are they complete? Do all of them sufficiently encompass the whole realm of self-development? That proof is not clear to me still. But at this point, it is an academic point. If I have an experience that shows incompleteness, I will spend more time thinking about this. Until then, I will continue to reap the fruit from the Pavlina Principles.