Noise, not grain - there are important differences. One of these is the fact that unlike grain, noise varies according to the colour channel. Usually the blue channel is the noisiest so one trick is to exclude this channel when sharpening. There are also a number of noise reduction plugins for Photoshop which use complex masking, blurring & sharpening processes (see www.fredmiranda.com for example).
And there is the standalone app Neatimage
which does a surprisingly good job - there is a free demo if you want to try.
Note that none of this applies to film grain - not quite sure why, but I suspect its to do with the fact that noise can be more readily isolated because the effect varies across the different colour channels and to some extent can be distinguished from genuine image data. Grain, on the other hand, once scanned is an integral part of the picture occuring in all channels equally. Having said that note that Neatimage can be used to reduce scanner noise often found in the shadow areas of scanned slides and prints.
Clever though this technology is, I don't think it matches shooting at a low ISO - which is my preferred approach. But noise reduction filters should be in any digital photographers toolkit for those times when high ISOs are unavoidable.
Colin K. Work, Pixstel