I have had much trouble with VueScan on a dual processor Mac running OS X (probably 10.2.8 at that time). There is much to like conceptually in this software. VueScan certainly has all the right tools built in (the developer actually listens to the users.. what a concept!).
I am interested in hearing from Mac OS users who are successfully using VueScan in Mac OS X. If it is running properly what is your hardware configuration? Which version of OS X are you using?