I bought this e-book, and I have to say its by far the best book I have found on guitar theory. I've learned a heck of a lot from it, and I often refer back to it as it serves as an excellent reference material.
Its very well written. Justin explains things in a very clear and concise manner and it cuts out the crap that other books generally have. Plus by buying it you are supporting this site, and as users of this site I'm sure we are all in agreement, we get a heck of a lot for free from this site so by giving something back we help keep it free and enable Justin to continue to help us along our journey of learning the guitar
I would recommend it to anyone. Excellent resource!