Comment 1 for bug 747611

This is likely a consequence of bug 742213. Your touchpad can give only pressure information, but pressure data is not reliable enough to be used by out of the box. For a while, Natty used the pressure data by default, but this has been reverted due to a report of spurious right click behavior.

You can restore the previous functionality in two ways:

1. At runtime by running: "xinput set-prop 'SynPS/2 Synaptics TouchPad' 'Synaptics Two-Finger Pressure' 29
2. At X startup by putting the following in your /etc/X11/xorg.conf (create it if it doesn't exist):

Section "InputClass"
        Identifier "touchpad catchall with default scroll"
        Driver "synaptics"
        MatchIsTouchpad "on"
        MatchDevicePath "/dev/input/event*"
        Option "EmulateTwoFingerMinZ" "29"
EndSection

Because this is the intended result of the change to synaptics, I'm marking this as "won't fix".