John
Just to make this completely clear. USM is the last thing to be done when processing an image. So if you want a printable and a web version save your file as TIFF or
PSD or DNG format BEFORE USM. Then resize it for the web in photoshop via the image size menu - do not use save for web. Having resized it apply the USM. Then save as jpeg then close without saving any more changes.
Next reopen the copy you saved earlier, apply USM and save in what ever format you want for printing. Result is you have two different versions which have had USM applied when they are at their final size.
Save for web, while easy has its flaws and this is one of them - another is it trashes EXIF data.
If you use Nikon Capture this USM trickery is not necessary as it applies the USM when saving the file each time (it stores the settings in the NEF rather than applying them).
Hope this helps.