The amount of sharpening depends on the sharpness of the scanner. I sharpen my Premier drums scans at 100-275, with a radius of .2. Some times I sharpen with High Pass, if the image itself needs a boost.
I think the attempts a some sort of rule here is incorrect. There are too many factors in play...
Lenny
Again, I have to agree with Lenny. Not only is the equipment used in the initial capture a major factor, but so is the size of the original, the subject matter, image tone, and print size.
When I was comparing scans from an epson 750 to the screen 1045 drum scanner, the epson needed to be sharpened to about Amount: 250 Radius: 1-1.5 and Threshold: 0-3 to attempt to match the native sharpness of the drum scan. Not to say that I was able to match the detail recorded in the drum scan, but just the feeling of edge definition. See this post
Dead Link Removed
Of course, it is impossible to tell for certain without seeing actual prints or files to compare, but by reading some of the sharpening settings here makes it sound like most people tend to over sharpen their images in photoshop. Ten years ago people went buckwild with the USM filter just because they could, and I think that played into a lot of the criticism of digital prints early on, and that continues to have negatively impact the acceptance of inkjet prints in the fine art market. That might be lessening now to some degree that people are more aware of the issue and as sensor sizes and resolution increased, and that editing programs enable 16-bit processing and printing.
With digital capture it can be much harder. When importing into Lightroom—I Shoot landscapes primarily—I bump the clarity up to 10-24 and then in sharpening i use Amount: 24-36, Radius: 0.5, Threshold: 0 Detail: 20-36. Anything more than that starts introducing sharpening artifacts.
Now that I am using Capture One for my raw imports/developing the sharpening settings seem to be better at higher levels before introducing artifacts. Amount: 100-180 Radius: 0.4-0.8 Threshold: 0. I also turn noise reduction down to the minimum possible so I don't have the effect of smoothing the edges as then trying to resharpen them. I think the combination of noise reduction and over sharpening might play into the unnatural look in a lot of digital prints.
To sharpen for printing I use the following workflow in photoshop. I copy the final flattened layer twice and then apply the USM at different amounts for the highlights and shadows (on the two separate layers), which are then set the lighten and darken blend modes. Then you can adjust them to different opacities to feather the amount of the adjustment. This is basically what the smart sharpen filter does, but I've found this method to be much faster than figuring out the smart sharpen tool and waiting for it to process, especially when working with large files.
Here are the ballpark settings, but each image is different and you have to develop your own judgment for these things.
Top Layer: Lighten blend mode: Opacity at 40%-60%, Amount: 120-150, Radius of 0.3-0.7 Threshold: 0
Middle Layer: Darken mode: Opacity at 50%-75%, Amount: 100-150, Radius of .8-1.2 Threshold: 0
Background: No USM
My best advice is to set the zoom to the print size, then click once to zoom in slightly so you can see the amount of the effect at print size, and what is happening at the pixel level when you are using the preview box in the USM window.