I'm fairly new to PHP, having implemented a couple of basic features in one of my websites. That said, this book is an invaluable aid, complementing the online PHP manual as a useful, concise reference guide. It not only covers the language core, but also looks at PHP extensions. Covers how to install PHP5, object-oriented PHP, file and string manipulation, HTML forms and other topics such as XML and multimedia.
As with all O'Reilly books, this one is liberally strewn with excellent examples and clear diagrams, and is well written for its target audience. It does presuppose some knowledge of basic programming concepts such as variables and loops, but would still appeal to the beginner as an addition to the online user guide.
Definitely recommend this book.