I'm always wary of books that have to congratulate the authors by having their photograph on the cover - and this one has five!
This book is an excellent beginner's tutorial with concise and clear examples throughout. But as this is roughly the 15th language I've learn't the lack of depth became very frustrating quite quickly. This carries over to the other topics they touch on: their superficial brushing off of concerns about cookies is *very* annoying. The authors really need to read "Philip and Alex's Guide to Web Publishing" to find out why cookies really are bad (an excellent book, although the author's picture on the cover, with his dog, does warn you of the occasionally self-absorbed content).
"Professional PHP" does have a reference section where the functions are grouped by category, again excellent for beginners, but there's no full, alphabetical, function and variable index in the back! If I know the function I want to use, but need to remind myself of the argument ordering etc. it's extremely labourious and frustrating to thumb through the pages of reference looking for the right section. I notice that O'Reilly now have a pocket PHP reference which may solve this problem.
Personally I'm still looking forward to the O'Reilly "complete reference" treatment whenever they get around to it.