This book is for you if you want to learn how to correctly debug some programs. This includes programs you've got sources for, as well as programs that you don't have source code for, like proprietary programs. Also, you should read this book if you want to run linux on a Non-PC compatible architecture. It describes how to use the hardware, how to interface to it's PROM/console functions, how to start the bootloader and finally how to load the Linux kernel. There is, however, no attempt to tell you how a given distro works.
There was a simple motivation to write this guide. I'm using Linux for nearly ten years now and learned a lot. There were things I needed to know, so I started to figure out. Other pieces of information were gained during everyday's work. But after all, it was hard work. Sometimes, it was just a matter of finding appropriate descriptions on the web, sometimes it wasn't that easy because nobody cared to describe how things work. Especially using rarely used computer's firmware consoles and the process of booting a Linux kernel on those machines is not all that easy to find, just because there's not a that large userbase and because these machines are just rare.
On the other hand, this rareness and lack of documentation is what many people keeps away from running Linux on Non-PC computers. Lack of people results in more bugs on those platforms, resulting in even less people that want to use those...