I bought Ken's book a while back. As Ken has mentioned in reference to that book, his memories of things aren't as clear as they used to be. It's a long time ago. Still a great read though. I enjoyed it.
I have also read "The Sierra Adventure" by Shawn Mills. That's another great book, in fact it has some quotes from various people that I hadn't seen anywhere else. I loved some of the inside story from Doug MacNeill in regards to the original King's Quest project.
I've actually been working on my own book in relation to Sierra, AGI, the AGI games, the tools, the fan-made games... all things AGI I guess. Its probably still a few years away from release though. I keep getting distracted by things like writing the web based AGI interpreter.