I've just discovered a great column about PhotoShop called "Out of Gamut", written by Bruce Fraser on creativepro.com. This particular column (there are many in the archive) has some great techniques for selective sharpening that avoids those crunchy, over-sharpened artifacts.
A lot of the advice here is not specifically needed for web work, but more appropriate to printing. However, if you do web graphics where appearance matters a lot (like selling fine art or photography) this stuff is manna. And I often do graphic work that will be used in both print and on-screen, so this stuff is exactly what I need.