Have you upgraded to Ubuntu 11.10 Oneiric Ocelot, but your touchpad seems not working after this upgrade. The touchpad will work only at the login screen. If this is the case, then you may try to enable it using the Configuration Editor (dconf Editor).
Open the terminal and install "dconf-tools" with this command:
sudo apt-get install dconf-tools
Via the Unity Dash, launch "dconf Editor":
Navigate now to this path:
org > gnome > settings-daemon > peripherals > touchpad
On the right pane of the window, check on "touchpad-enabled" to enable it:
You can also disable the touchpad while typing by enabling the "disable-while-typing" entry:
After you finish close the editor, no reboot or logoff is required.