I used to be an application programmer, but for the last several years AWK (and, much less frequently, SED) has been one of my favorite tools. There are many, many, situations where an AWK/SED/sh pipe has a small fraction of the code size of any other way of solving the problem. In addition, AWK (specifically GAWK, which is the baby of Arnold Robbins -- one of the authors of this book) is extremely efficiently implemented, and so AWK scripts are generally faster for their chosen tasks than similar programs in perl, python, whatever.
This book gives an excellent tutorial introduction to all of the features of these languages, but (to answer the whining, er, constructive criticism, of some of the reviewer) it is not going to tell you how to solve every problem you ever encounter (that is why you have a brain). The way to use the book is keep it on your desk while you play with the tools it describes.
As a reference, the GAWK reference manual (written by the selfsame Arnold Robbins, and available for free from GNU) is much more complete, so I strongly advise the reader to keep it close at hand (which it always is, through the magic of online search).