I used the preprint version of this book for my mechanics class, and it is excellent. It is not for the faint-of-heart or those who have never been introduced to physics before. This book tackles the problem of teaching physics by an examination of physical phenomenon through intuitive understanding and exploration of limits. It doesn't really help those who want to pass standardized exams, but I think it really helped me to understand mechanics and special relativity (better than I would have otherwise, in any case).