Readers already familiar with Perl will presumably either own Programming Perl or have decided not to buy a copy, since it seems to be the only reference for the language. (It is certainly the standard one.) If you are thinking of learning Perl then you have a choice between using this book, using the companion volume Learning Perl, or hacking it out for yourselves with the aid of the fairly comprehensive manual entry. Programming Perl worked fine for me, and it's probably the right way to go for anyone who can already program in C or shell. On the other hand, Learning Perl looks like a good textbook, and its existence makes Perl a suitable first language for those people who want to be able to write general purpose programs for their own use, rather than for commercial, scientific or esoteric theoretical purposes.
The first two chapters of Programming Perl provide a basic introduction to Perl. The third and fourth are basically reference material, going in some detail through the syntax and semantics of the language and describing all of the functions available. The fifth and sixth chapters contain examples of useful Perl code fragments and real programs. The last chapter contains everything else. The appendices — a BNF style grammar of Perl and a description of the Perl library functions — improve the book's value as a reference, while the glossary will be helpful for those without a Unix and C background. Everything is liberally illustrated with examples, with the occasional redundancy doing no harm. The authors' sense of humour is always present, and they certainly don't take themselves too seriously — Perl is the "Pathologically Eclectic Rubbish Lister", and the three cardinal virtues of a programmer are "laziness, impatience and hubris"!
As with all the O'Reilly books, the layout and formatting are clear and the binding and paper are top quality. At sixty Australian dollars, Programming Perl is fairly expensive (though it's presumably cheaper in the States), but just think of it as a contribution to Larry Wall for making Perl freely available in the first place.
Note: a third edition of Programming Perl is now available.