After installing Mountain Lion 10.8.5, I have a slightly different Magic Mouse preferences window than I did with Snow Leopard. There is no longer an option for entirely turning off scrolling. This is really annoying while working in Photoshop as the cursor will periodically "jump". I also do not have "Universal Access" in my System Preferences. How do I turn off scrolling?
This was driving me nuts, too. Finally found the solution:
System Preferences > Accessibility > Mouse & Trackpad.
Click "Mouse Options" in the bottom right. Unclick the box that says "Scrolling."
Now I can play League of Legends again without pinging the screen a billion times.