If you do websites for a living, and better yet, if you do medium-sizes one, this is a book to read. It packs an amazing amount of info, covering topics from development environments, i10n, L8n, and data integrity, up to bottlenecks, scaling web applications and statistics, monitoring and alerting.
I'm picking up a lot of good tidbits and validation. At work, we where naturally moving to a deploy process very similar to the one described in this book. The use of SCM systems, and the integration of those with a ticketing system and Wiki are also gaining grown there.
I'm at the end of chapter 6, about Email, but I did a fast read over the entire book first.
Definitively, highly recommended.