As someone that has just spent the last 27 months building an OS from scratch in a University research environment (an OS that can survive catastrophic hardware and software failure ), I am very impressed with the quality of this document. I only wish I had found it previously!
OS dev can be great fun and gives you a level of understanding about how computers actually work that is hard to gain from other sources. I have frequently found myself using the knowledge I gained from building the OS when working on other projects. It has been particularly useful when it comes to understanding performance issues. I would highly recommend it to anyone that is even remotely interested.
Other superb resources to help you get started include the OSdev wiki, along with this document from the University of Birmingham, UK.
Last week I read the very good 'How to build an operating system from scratch' , and I'm glad I did. It meant that I could burrow into the files on this github project and understand exactly what was going on.
One day, when I finally have some free time, I am totally going to do this myself.