This is such an important subject! I didn't really know anything about rendering, values, edge control etc until my design class in animation school started. Wow, did that drive it home. We were drilled on "organize your values, keep the gradients moving you around the picture, stack your values within the gradients". Rinse and repeat.
I'm still a long shot from having mastered these skills, but tutorials like these are really good refreshers and clarify so many questions that come up later. Thanks a lot for this, it's a great learning tool! Certainly deserved its DD.