I suspect this behaviour is caused by the interaction of a couple of
factors:

* the touchpad is anisotropic, about 2500DPI vertically but only 1500DPI 
horizontally
* both the synaptics driver and X are making making pointer acceleration 
calculations

These can be mostly fixed by tweaking the config; I'm currently using
(add this as "/etc/X11/xorg.conf.d/50-touchpad.conf" and restart your
Xserver):

Section "InputClass"                                                            
                                                                                
                                
        Identifier "touchpad"                                                   
                                                                                
                                
        MatchProduct "SynPS/2 Synaptics TouchPad"
        Driver "synaptics"
        # fix touchpad resolution
        Option "VertResolution" "100"
        Option "HorizResolution" "65"
        # disable synaptics driver pointer acceleration
        Option "MinSpeed" "1"
        Option "MaxSpeed" "1"
        # tweak the X-server pointer acceleration
        Option "AccelerationProfile" "2"
        Option "AdaptiveDeceleration" "16"
        Option "ConstantDeceleration" "16"
        Option "VelocityScale" "32"
EndSection

See also:
https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-input-synaptics/+bug/621432


** Attachment added: "50-touchpad.conf"
   
https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-input-synaptics/+bug/1042069/+attachment/3402410/+files/50-touchpad.conf

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which is subscribed to xserver-xorg-input-synaptics in Ubuntu.
https://bugs.launchpad.net/bugs/1042069

Title:
  Jumpy Mouse Cursor using Thinkpad X230 Touchpad

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https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-input-synaptics/+bug/1042069/+subscriptions

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