You can get VERY clever with unsharp mask - moving to LAB is one way, however, mode changes do result in small erosions of quality. Another way to sharpen in RGB without colour issues is to apply USM
, then go to Edit->Fade and select luminosity - exactly the same effect as LAB but without having to switch modes.
Jeff's technique is very good for selective sharpening. Indeed, many professionals do ALL
image mods through duplicate layers of one sort or another - takes a little while to get your head round all the possibilities of layers, but an enormously powerful technique.
You can also look at channels - quite often one colour channel will take more sharpening than another.
Not sure about incremental sharpening though - all sharpening creates artifacts of one kind or another, so by working in increments you are in effect sharpening previously created artifacts, and you'll reach a limit much more quickly. Taking this logic further, recently I've been working on images starting from 0 in camera sharpening (turned off in RAW conversion). I've found that while the files start off looking very soft, they accept USM
sharpening much better.
Colin K. Work, Pixstel