I finally got around to trying focus stacking with scans from my CoolScan IV (which has driven me nuts trying to deal with shallow depth of field throwing areas out of focus if the film is not very very flat, a particular problem with transparencies, even though I remount them to scan in mounts with pegs for the sprocket holes to try and pull them flat), and first results are very promising. I started by measuring focus distance at different points on the transparency to determine the overall range of focus, and then using manual focus settings, scanned a series 10 focus units apart inside that range, which gave me 3 scans.
I opened all the NEFs in ACR 64-bit via Bridge, made all adjustments to one, and synced the adjustments to the others.
Then I went into CS5, and opened the NEFs into a stack with auto alignment. I created masks for the top two layers for each layer and with a medium feathered brush painted out the portions where the film grain sharpness had fallen off, making sure some of the live areas overlapped.
Result seems to be an image with crisp grain everywhere. I have yet to print, but I don't see any artifacts on the screen.
Happy camper so far.