Good questions, but no. Almost all of what you see as sharpening is in the "L" channel. That's why you only sharpen it. The "a" and "b" channels don't have any lightness or gray information. They give nothing to the contrast that you use for seeing sharpness. Your eyelashes are almost completely in the "L" channel.
Take a look at these channels some time. You'll have a tough time figuring out what the shapes are in your photo. If the colors aren't one of the 4 extremes of the two axis (blue and yellow / magenta and green) and saturated you'll have a tough time even seeing anything at all. Well, as far as easily recognizable things go. I bet you can't even find the eyelashes in the "a" and "b" channels. After spending some time with these color only channels, you'll loose the concept of "color detail"; the "detail" is in the lightness and not in the color.
Also remember that "Surface Blur" looks for the edges and avoids them. It really only blurs the fields where everything is pretty much the same - based on the threshold setting. So, it would be blurring the inside of a big magenta field of color, but not the edges with the greens.
For fun and learning, try blurs other than "Surface Blur". These will blur the boundaries of colors. I think you will be surprised at how little these will affect the "sharpness" of your photo. Oh, you can really over do it and see what odd things you can get. That is why you use "Surface Blur" though; you don't want to blur the boundaries.
You will be surprised at how much blurring you can do with "Surface Blur" on the color channels. Where this really shines is with human skin. As you crank up the blur radius you will see some very nice softening of skin colors. My experience is that you can get a variety of effects at different levels - depending on the lighting. This can be a very nice tool for portraits of women. This is a benefit of this technique far beyond just getting rid of chroma noise.
So, give it a try and see what you can do with it.
Clyde
Doesn't the blurring on the colour layers "smudge" the colour boundary and thereby lose sharpness?
For instance, it sounds as if the transition between eyelashes and skin would soften and the skin would pick up some "gray" from the lashes, or fine colour detail would be reduced even though the lightness (luminance?) contrast is maintained.
Andy
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