The 4-Hour Workweek really comes down to one thing: successful use of Pareto's Principle.
Roughly one third of Tim Ferriss' book reads like an infomercial but one can see example after example of how applying Pareto's Principle to everything we do in our work and personal lives gives us the opportunity to maximize our return on effort.
In the interest of being brief, here is my distillation of the key points raised in The 4-Hour Workweek:
Some other useful things you'll find in this book are various websites and services which are listed in each chapter with reviews, helpful hints and potential pitfalls, so that you can make immediate use of the strategies you're exploring.
If you are a person dedicated to getting things done I'm not sure that The 4-Hour Workweek holds an abundance of wisdom for you since you likely already employ many of the concepts in the book. One of the major weaknesses of the 4-Hour sales pitch is the assumption that everyone detests their job but lacks the creativity or desire to do something about it. The concepts and habits that Mr. Ferriss asks you to adopt would be quite unmanageable for most people, in my opinion, because they are too aggressive and emotionally uncomfortable.
A few weeks ago I attended a local Chamber of Commerce meeting and one of the attendees joked that she had received a copy of 4-Hour Workweek several years ago as a gift, had read a few chapters, and the book still sits half-read on her nightstand. During this time she has grown her educational services business from a one person operation to dozens of employees, with recent state accreditation. She enjoys what she is doing and has no need for the deceptive escapism that is often part of the 4-Hour plan.
The 4-Hour Workweek has plenty of interesting things to say but I would advise you to figure out what it is you love to do (Eustress), and go do that. The rest should follow.