I first ran across this book a while back, when I was involved in Buddhism in a sort of academic way. The Three Pillars of Zen was on the reading list for one of my classes, and I ended up reading it the way I read most academic texts - with an eyes towards extracting pithy quotes and supporting ideas for an eventual paper. At the time, it made little impression on me, although I think I may have footnoted it a couple times in assorted papers.
Then, about two years ago, I began to rediscover Buddhism (and, in particular Zen) not as an field of intellectual study, but as a practice and a way of life. I began regularly sitting - first five minutes a day, then ten, then half an hour - and occasionally sitting zazen and attending dharma talks at one of our local Zen centers.
But I still didn't really have a good grounding in some of the fundamentals. Yes, I knew the basic dharma, but I felt that I was missing something.
Enter The Three Pillars of Zen. I don't know why I happened to grab it, but it proved to be exactly what I was looking for - a good introduction to the fundamentals of Zen, with a particular emphasis on practice. Reading this gave my sitting practice something to take root in, and has offered me continual inspiration.
There's a lot here, and a lot to absorb, and I don't doubt that different parts of this book will speak to different people. For me, I found the depictions of assorted enlightenment experiences to be incredibly inspiring, but the real meat was in the collection of student-roshi interviews. I found every doubt, every question that I've had about my practice repeated, in some cases word-for-word, in this section - which was a nice thing to encounter, as a relative neophyte who is, admittedly, plagued with doubts as to virtually everything.
I would neccessarily reccommend this to someone who knows nothing of Buddhism or of the dharma, but I would reccommend it as an excellent introduction to Zen and the practice of Zen. It's a book that I return to every day, and that I find a continual source of inspiration.