Seth Goodling, on his GTD-modded notebook:
"I use two versions depending on my mood and time. If I am feeling crafty, I grab about 20 pages and make notches down the length of the book with a razor blade to create little tabs to separate my sections. If time does not allow, I simply grab those pages and use a marker to color a section.
I should run over with my car. It works for me, I tend to just keep the "chapters" straight in my head…."