I was very pleased with this book, having spent many hours trying to find this sort of information in an understandable and comprehensive format on the web. The book is everything I'd hoped it would be, and my website now runs much faster as a result.
However, after buying the book (and paying for shipping to NZ, which is around the same cost as the book itself) I was not that thrilled to suddenly find "articles" popping up all over the internet basically quoting the entire book verbatim. Save your hard-earned cash and just google it.
"The author's core ideas are clearly explained; the performance improvements are demonstrated; the book's production is excellent. High Performance Web Sites is highly recommended to all Web developers seriously interested in improving their site visitors' experiences."
--Michael J. Ross, Web Developer, Slashdot.org