In a thread about sharpening, I must admit to some surprise to seeing no mention of Bruce Fraser's Real World Image Sharpening book, where he describes the 3 stage sharpening protocol very clearly. Capture sharpening to remove the effects of digitizing and anti-aliasing; creative sharpening to emphasize certain parts of the image (soften skin, sharpen eyes, add local contrast, etc); and finally, output sharpening for your specific media. Bruce has calculated the maximum amount of sharpening to can apply to get halos to exist just below the threshold of visibility, which means that your image is as sharp as it can be without looking "digital" ...

I find this prototol really changes the way you approach sharpening. Nothing ever feels random about the process, especially if you use PKSharpener from Pixel Genius. This plugin implements all the different options in Bruce's book.

What I do to handle different media from the same image is to save an intermediate version with all my edits, then make two version ... one for the web, which is output sharpened at 800px, wide, medium, narrow or superfine edges depending on the subject; and one for the size of print, say 12x18 upsized to 300ppi then sharpened using the contone (continuous tones) setting for 300ppi glossy. Matte uses slightly more sharpening because ink tends to bleed more on matte surfaces.

I've found that my prints look consistently sharp and my web images have stopped looking over sharpened.

For upsizing, I use the excellent DOP_Upsizing automation plugin that implements a form of stepped bicubic with intermediate sharpening. It retains detail better than any other method I've used. There is an interesting companion article on that site to go with this (free) plugin. Digital Outback Photo by the way.

Hope that's of interest to some.