Works as good as every version of Logitech software I've used, going back to the old ADB MouseKey stuff. Currently using USB Wheel Mouse (M/N: BB48) on a G4 350, OS9.2.2. Same mouse for 2 years with several versions of MouseWare and OS. No problems at all. I tend to forget about the "Web Wheel", but I can see how it could be useful for some. I spend most of my time in OS X, where the mouse just "works" (without Smart Move and application awareness being as there is no driver yet, but right click performs "cntrl-click" and the scroll wheel works), but when I'm in OS 9 the MouseWare works great.