After installing ubuntu-gnome-desktop, it seems to replace the touchpad synaptics drivers. Weird…
The touchpad works fine on gnome afterwards but on Unity, it acts as if the drivers aren’t installed.
I found this quick fix (took me an hour) on an Arch Linux forum post (I think).
Copy this file:
cp /usr/share/X11/xorg.conf.d/50-synaptics.conf /etc/X11/xorg.conf.d/50-synaptics.conf
If the directory doesn’t exist:
Reboot. Hope this saves you some time.