Installed no problem. Restarted and everything works fine including horizontal scrolling ( shift + scroll) as before ( was not expecting that after what I read here!). I like the vertical scroll speed adjusting slider which works great. The Help loads very fast ( I assume read from the HD rather than from a web site) for me and was thorough and useful. It includes some comment on horizontal scrolling built into some keyboards etc so you may want to check it out. Accelerated Scrolling option when selected also seems to work better than before although it takes some getting used to. Only thing I notice is that 'Microsoft Mouse' pops up often in the Process Listing in Process Viewer. And wish MS would give us a clue as to updates, bug fixes etc. No readme included. For info I have Dual 1 Ghz G4 Mirrored with 10.2.6, 768MB. Intelliimouse Explorer USB. Personally I respect MS for still producing software updates for a (nearly) 4 year old product. I could never do without the 5 button options especially for gaming.