I am currently using a Microsoft Intellimouse Optical with Mountain Lion. The latest Microsoft driver works, with one caveat - I have to go into System Preferences every time I boot, and click on "Microsoft Mouse" to activate the driver. Its a bit of an annoyance, but I love this mouse. I program the side and wheel buttons to do various things like close current browser tab/window and move "back". I guess its a longshot, but does anyone know if this still works in Mavericks? I'm hesitant to upgrade because of this (as well as some other app compatibility).