It's said that "the best way to learn something is to teach it to someone else", and I think there's a huge hunk of truth there!

I don't use your method to help digest books, but I use it heavily when I'm working through a particularly difficult programming problem. And I've found that the less the person I'm explaining to knows about the subject, the more effective the process is. I think it's because it forces me to break the problem down to the bare fundamentals so they can understand what I'm saying.