This book is about 17 years old which means the knowledge is in the neighborhood of 20 years old but really it is much older. Why read it? Because this is as or more relevant now, 2016, than it was in 1999. I tend to be a bit biased to some older books and this one is no exception. Why? Because it was written before books became the trendy thing "to do" because it was great for marketing. Any chance you have to learn from a practitioner you'll be better off than reading what some college professor or researcher or worse, someone who is just trying to market/brand themselves.
More signs of a good book; If you can take it's content and apply it to the current times and it will still produce profits. Want more? Although he might have been slightly off on a couple of things, a good chunk of this book is essentially Mr. Godin looking into a crystal ball and describing the future.
A great intersection of past knowledge, current trends(circa 1999 but still relevant) and a wonderful philosophy, compiled by a human being that repeatedly helps makes humanity better.