I use the raw sharpening tosharpen the image to the extent that you don't see the pixel structure emphasized. It seems to be a fairly fine (i.e., high spatial frequency, as Daniel would like to say) device that can actually compensate for the lack of sharpness of a lens, or compensate for softening caused by anti-noise filtering, which is also fairly fine filtering. I tend to RAW sharpen with a 100% view of the sharpest area of the picture until I notice sharp transitions in the pixels, then back off. I then apply any noise filtering as judiciously as I can, and then perhaps go back to the raw sharpening if need be. It usually ends up between 1-5, (lower usually with lower ISO) but I've gone higher, particularly when I've got aggressive noise filtering.


The RGB sharpening seems quite different to me. It seems to enhance contrast in broader areas along edges, to make a picture look subjectively sharper, regardless of if you're looking at it at 100% or not, while the Raw sharpening tool is pretty much unnoticeable if you're looking at it in a 'fit to window' type view. If you overdo the RAW sharpening, things look too pixel crunchy. If you overdo the sharpening the the RGB tab, things just look ridiculous.