This book has proven quite handy of late. I flip through it’s pages at least once a day, and quite often more than that as I’m building my personal site as well as a couple of sites for clients. I have a pretty solid foundation in programming concepts from Perl and JavaScript as well as PHP, so I am using the book as a reference manual as opposed to a linear text-book. There are some concepts which I’ve had to look up on the Web as they were considered basic knowledge.
I recommend the book for those who are comfortable with some programming, but not those new to the language.