I routinely find myself attempting to scroll horizontally, or diagonally using the mighty mouse’s scroll ball, only to see(again,) that it doesn’t work. Though only affecting a relatively small group, I’m sure those involved would find that functionality quite useful!
to help us help you, start up a terminal (Applications -> Utilities -> Terminal). at the command line there, type
move the mouse pointer into the xev window that is created. now play with the mighty mouse scroll ball. move the mouse pointer out of the xev window back to the terminal. press ctrl-c.
now cut-n-paste a good size chunk of the stuff that showed up in the terminal window, and post it here.
the horizontal movement of the trackball produces no data in xev. i guess we’re a bit out of luck then?