I'm having problems with my MacbookPro1.1's trackpad under Ubuntu 12.04. Whilst moving diagonally, it wiggles from side to side, as if the trackpad's X and Y are conflicting. Also, if I move my finger on the trackpad in a perfect circle, it moves in a square-ish shape, like a circle with semi-straight sides. What do I need to install / change?
It's not Ubuntu specific, I see the same behavior on a Macbook 2,1 under Fedora and Mint. In fact, if you observe the behavior of the cursor when booting the MacBook into the boot selector (prior to OSX loading) you'll see something very similar, if not the same... I suspect the pad itself is only capable of generating these movements and then OSX is just really good at smoothing them out into what looks diagonal.
Wish I knew a fix, sorry.