This book won't make you into a wizard like the one you see on the cover. What it
will do is open your eyes.
I mean, it teaches scheme for Pete's sake. Playing Devil's advocate here, who honestly uses that in pratcital everyday systems? Nobody reads the book and immediately goes "Wow! Now that I learned Scheme, which is totally the best language, I'll use my Scheme powers to create the coolest software in the world!"
The reason why this book is so cherished is because it treats scheme as a building block for implementing the most interesting ideas and patterns from systems you use every day.
Rusty on recursion? That's chapter one. You'll be thinking with recursion and will understand most of its implications by the first few dozen pages.
Think you know about OO? Build your own object-orientation system in Chapter 2. Yes, on top of scheme.
Write your own programming language (well, implement eval anyway) in a few short pages in Chapter 4. (The result is about thirty lines).
How do Von Neuman register machines work? If you don't already know, you'll be writing a simple compiler in Chapter 5.
This up-close-and-personal whirlwind tour of these important CS concepts was very enlightening to me when I read it. This book isn't about how to learn languages; rather, it's about working with ideas: why abstractions are important, how to reason with them, and how to implement them using whatever bare tools you've got.
(Schemers: before commenting, realize that i wasn't poking fun at our favorite language; rather, i'm merely asserting that scheme isn't the point of the book)