The Black and White Adjustment Layer has a nice ability to target and boost or suppress narrowly defined hues. For example, it can affect red without affecting yellow. That's something you can't do with curves.
In this video I'm experimenting not with what kinds of black and white images can be made from the Black and White Adjustment Layer, but what kinds of color images can be made using it.
related:
Technicolor 2-Strip Process in Photoshop
FOLLOWUP: An Experiment with Selective Color Adjustment Layer
I'm curious to see if all I did above was recreate Selective Color the hard way. It looks as though there is some overlap, but Selective Color is not as aggressive in being able to change the image.
UPDATE
Photoshop Black and White Adjustment Layer: A Closer Look
UPDATE 5/31/2009
The Black and White Adjustment Layer
reconstructs the red channel of an image as follows:
R 100% and its 2 red-containing companions, Y and M at 100% - all else at 0%
reconstructs the green channel of an image as follows:
G 100% and its 2 green-containing companions, Y and C at 100% - all else at 0%
reconstructs the blue channel of an image as follows:
B 100% and its 2 blue-containing companions, C and M at 100% - all else at 0%
UPDATE 5/31/2009
The color photography of Madame Yevonde
