The fix from bug 125550 disabled horizontal rubber-banding without a horizontal scrollbar, because it is very distracting. But it was reverted again with bug 127521.
Beth Dakin suggested in bug 125550 to open a bug report for discussion / input.
For me from a user view: With the Magic Mouse it is really hard to scroll only a little bit, without to see the effect of horizontal rubber-banding. (Because I never have the finger on the mouse for a perfectly diagonally scroll down.) Same issue with the trackpad, when the MacBook is on my lap.
Maybe it could be solved like on iOS. There, when you start scrolling, a sideway scrolling is blocked. What do you think ?
Thanks in advance.