The silver anniversary edition is an updated version of the classic work originally published in 1971. How can this still be relevant? Easy: people haven't really changed.
Weinberg did something courageous in his updated text. Instead of whitewashing history, he let his original text stand, unedited, and simply commented on each chapter separately. The approach worked for me, making an already entertaining text a joy to read.
What is all this about? Weinberg writes "This book has only one major purpose--to trigger the beginning of a new field of study: computer programming as a human activity, or, in short, the psychology of computer programming. All other goals are subservient to that one." Indeed there has been much study of computer programming as an art and as a discipline for individuals and for groups. This book may represent the beginning of that noble effort.
Don't be put off by the technology Weinberg occasionally uses within the text. At the time of this book's writing, FORTRAN, PL/1, and APL were in common use and OS/360 was the defacto standard. If echoes of the past bother you, ignore them! Instead, concentrate on Weinberg's main topic: the people who develop software systems. For example, consider the following: "...the average programming manager would prefer that a project be estimated at twelve months and take twelve than the same project be estimated at six months and take nine. This is an area where psychological study could be rewarding, but there are indications from other situations that it is not the mean length of estimated time that annoys people, but, rather, the standard deviation in actual time taken." Of course this notion applies as much today as it did then. Weinberg provides numerous, powerful insights throughout the text that have stood the test of time. He got it right then--and it is still right.
The book is well researched and contains many stories. All ring true and some made me laugh out loud. If you don't see a little of yourself in this book, you aren't a computer professional. Buy it, read it, and then leave it on your manager's chair. It will do both of you a world of good.