There's a huge difference using my mouse in Plan9 than in Plan9port on my mac. Plan9 feels almost unusable by comparison. I suspect much of this is the very finely tuned acceleration/fine-pointing behavior of the mouse on modern desktop platforms.
That's probably a ripe space for improving the Plan9 user experience.
I wish there were better accessibility solutions for Plan9 as regards the mouse. That's likely another ripe area for tuning - taking advantage of Fitts' law in UI interactions (with a real acceleration/precision model) would be nice. There's few enough UI elements in our toolkit that it might even be feasible to do as a hobbyist.
Paul