Wow... that tutorial gave me an idea for something I haven't seen nor thought about before!
You said the black and white adjustment layer gives us access to all the channels... "levels on steroids" I think is how you put it.
Okay... add your black and white adjustment layer and click OK. Then change the blend mode of that layer to luminosity. See where I'm going? Sure you can drag the sliders BUT more importantly (the "on steroids" part) you can click anywhere in the image and drag to make different colors lighter and darker. I think using it this way could help out those really interested in the photo art type of stuff around retouch pro as I was getting some pretty crazy looking stuff while playing with it this way.
I love how you used the BW adj. layer to make a selection - that was something I hadn't thought of before either
