Here's a slight variation on Feivel's technique that I use often. I think that I picked it up from the luminous landscape site (smart sharpening).

Anyhoo--here goes:

1. Convert the image to lab color
2. Click on the channels palette and add a new channel. (You can title it sharpen mask if you want).
3. Click on the lightness channel and hit Ctrl-A to select everything.
4. Hit Ctrl-C to copy
5. Select the sharpen mask channel and paste (ctrl-v)
6. Run the find edges filter
7. Optional: use levels to adjust the black point
8. Apply a gaussian blur. I usally use 5 pixels.
9. Optional: use levels again to adjust the black point.
10. Go to select, and load selection. Make sure the mask channel is specified in the dialog box, and check 'invert'
11. Go back to the original image on the layers palette. The selection you have loaded will act as a layer mask controlling where the unsharp mask is applied.
12. Apply the unsharp mask filter as needed. You can use high values without much degredation or sharpening artifacts this way.

Hope this helps!

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Chewie