BCLEE  Nikon Scan 4 is incompatible with OS X 10.5 on either PowerPC or Intel platforms. For most users it just crashes or hangs up. I got it to stop crashing by uninstalling and reinstalling, but it locks up the computer while in use (USB input devices stop responding) and on my CoolScan 5000 is takes something like 30 minutes to scan a slide at my usual settings.

If you don't currently have a Nikon scanner, I would recommend against getting one unless/until Nikon starts supporting OS X again. If you already have one and you can't return it, look for VueScan or SilverFast.

I can only give this the worst rating -- even though I think some of the features are better than the third party software, I can't use them now so it doesn't really matter.  
(Version 4.0.2)