Like most I have been playing with this a bit to try and get the best out of the filter. I tend to find that Lens Blur gets better results than Gaussian Blur, though if the edges are not clean there can be some artifacts produced.
I also tend to set the shadow fade to 100% for 20% tone and radius of 3 to prevent sharpening in shadows where noise is greatest; and set highlight fade to 20% for 80% tone and radius of 5 to minimise sharpening of flat areas of texture. These settings help to constrain sharpening to edges rather than across every bump in the image. Using these settings allows a more aggressive sharpening percentage without creating halos or increasing noise in textured areas.
I have also been experimenting with multiple pass sharpening which iteratively can produce better results than a single pass of the sharpening filter; though it can be a balancing act to minimise halos across sharp edges where the tonal difference is high. Running the filter at 0.4/100, 0.8/30, 1.6/12, and 3.2/10 produces a very sharp image though halos start to crop up - it depends upon how objectionable these are in reality.
I find that post sharpening it helps to run the noise reduction filter as the sharpening process tends to increase noise in areas of flat tone. The noise reduction tool gently applied does a good of reducing the increased noise in flat tonal areas whilst still preserving the sharp edges created by the smart sharpen tool.
One final comment, the quality of the sharpening process depends greatly upon the quality of the interpolation of the original RAW file. In this respect ACR3.1 produces much better edges than any of the other RAW convertors on the market at the moment and can be sharpened to produce a much more detailed image. Whilst there are claims that C1 images are sharp, the images it produces contain a lot of 'zipper' artifacts along edges which when sharpened can produce nasty effects in the image.
