Have not read the book, but the vast majority of these books are garbage. As others have pointed out, minimize your expenses, invest at least 60% of your take home pay and you will be fine. I do not plan on working a day past 50 and am well on my way of getting there and have not read any of these books.
A really good forum on early retirment is at
http://www.early-retirement.org/forums/index.php
They probably have the best retirment calculator on the net as well called FIRECALC (although most calculators are garbage)