Edmond Desbiens , Oct 19, 2008; 12:04 p.m.
The newer philosophy and I believe the right one is to separate sharpening into 3 steps.
First a little about sharpening - Sharpening is a trick to increase perceived edge contrast lost due to the digitization process. You camera, when it digitizes the image, loses some of the initial edge contrast. Then when you print, the digitization to the printer will again cause lost edge contrast. If you do some heavy post processing, again you may loose some edge contrast.
So First step is to sharpen to compensate for the camera digitization. This will get the right look while editing your images. You need to do this only for Raw images this is done for you in jpg images.
Second step. If you do some heavy manipulation (e.g. resize for web) or want some special effect you sharpen again.
third step When you want to print, you sharpen for the printer. Remember, a correctly sharpened image for the printer looks bad on screen (the 2 output sources require different sharpening because of different digitization)
If you want a better explanation, check out pixel genius's web site they have a nice tutorial. I also use their software to make all of this really easy.