In a dual-monitor configuration (I happen to employing NVIDIA, but not sure it matters), want to both:
- display each monitor vertically, in "portrait" mode (rotated, with xrandr(1)),
- and make mouse movement/transition span horizontally between the monitors.
By "default" in vertically-rotated config, the mouse spans between monitors only from bottom of one monitor and top of the other. Extremely annoying, almost unusable.