Dated, yes. But that's the only weakness of this excellent book, which covers the philosophy and structure of userland in Unix, and it's not an important one -- nroff is still necessary for man pages, and life on the command line is something anyone dealing with a Unix box should get used to, whether the user is using a shell account on their local freenet or a cutting edge Athlon64 Linux PC or PowerMac G5. (Or even SCO, if you must.)
The tools covered are timeless ones -- make, lex, yacc, and others that are still important for software development some twenty-five to thirty years after they were first written. There's no networking, no Perl, and the shell language is ancient, but what's in there still works, with only minor changes to accomodate ANSI C (if you're using GCC, even that can be dispensed with using a compiler flag). The book also serves as an education in programming language design, working out a full programmable calculator system called hoc, and an introduction to the concept of toolsmithing.
This book and Kernighan's book Software Tools (coauthored with P.J. Plauger) provide a great education in how to build a computer system; there's a very good reason both books are still in print after many, many years when most computer books turn over editions every year or two. Whatever your Unix is -- Mac, Linux, Solaris, BSD, whatever -- take this book with you when you start hacking around on the command line. It's not everything you'll ever need to know, but it's one of the best to get you started.