Touchpad sensitivity scales to virtual screen dimensions

Not sure if you're still looking, but I found some info in these two threads: https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-input-synaptics/+bug/327428 and bug 591954. Turns out that the dimensions of the touchpad are being scaled to the dimensions of the virtual screen that xorg generates to contain your monitors. Since most people have their monitors side-by-side, you end up with a virtual screen that's probably twice as wide as you'd have with a single monitor, so your horizontal trackpad movements are scaled to be twice as fast. The fix was originally committed almost 2 years ago, which is a bit ridiculous, but...

What I've ended up doing is following the advice of the last post from the first thread and installing the xorg synaptics driver for oneiric from here: http://packages.ubuntu.com/oneiric/amd64/xserver-xorg-input-synaptics/download

This fixed everything up just fine for me.

xinput set-prop "SynPS/2 Synaptics TouchPad" "Device Accel Velocity Scaling" 10

(10 is the sensibility , you can tweak it). More info there : https://bbs.archlinux.org/viewtopic.php?pid=963650#p963650