Comment 4 for bug 727259

There's a workaround tool at http://sourceforge.net/projects/touchdaemon/develop which detects keyboard activity and disables/re-enables the touchpad accordingly. There's a patch posted there which is a good improvement, to use X calls instead of shelling out subcommands. Without the patch I had to fixup some string handling errors, and the invocation is messy, like this:
./touchdaemon -d -m 100 -c 'xinput set-int-prop "ImPS/2 Generic Wheel Mouse" "Device Enabled" 8'
instead of
./touchdaemon -d

(I ran the tool with a 100ms polling interval because the 200ms interval seemed to let the touchpad back in from time to time.)

To build the tool I needed
sudo apt-get install libx11-dev xserver-xorg-dev

I found the tool by seeing it mentioned here: https://bbs.archlinux.org/viewtopic.php?pid=733079