After upgrading from Ubuntu 10.10 to Ubuntu 11.04, my MacBook Pro's touchpad stopped working.
It works fine on the login screen, but after logging in it stops working.
(Answering my own question, in the hope that it saves someone else a bit of head scratching).
After the upgrade, your Gnome desktop configuration may have gone awry. There are a few settings which enable or disable the touchpad in certain contexts which may need tweaking to get the touchpad working again. Here's how I got mine working again:
HTH