Cypher,
I didn't see your post until just now, sorry!
As far as I know there aren't any books specific to this method. Some will argue that it's unschooling because it is in some ways child led. I don't agree. While I always gave my DS the opportunity to identify "what comes next?" I was clear that we would always be learning something. Unschoolers allow their kids to take days off if they don't feel like learning, and never place demands on material. Neither one of those is true of us.
When you first get started it seems like you spend a significant amount of time thinking "Oh, god, what comes next?'. Once you've been at it for a little while, things just seem to sort of flow naturally. A perfect example of this is "the great chicken project" currently going on at my house. It started as a lesson in politics for my 14 yo, moved into economics, the GDP etc. Now I have a 6 yo raising chickens for urban chicken farmers. He wrote a business plan, is calculating cost of goods and will ultimately realize a profit.
A lot depends on you and how flexible you want to be. How far to stretch the line. Some of the stuff that we do is not reasonable for someone living in a city, just as there are things that are hard for us in the boonies! If you are determined to do an hour of math a day, then it's hard to be flexible. But we found using this method that we hit every core subject every week. Just try it! After a while, you'll have lines going in 10 different directions. Some will die, some will morph into things you never expected and some will turn your DS onto things he didn't know existed and develop new passions.
