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. I'm a new user, so couldn't answer in a separate post for the next few hours).

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:

• Hit Alt-F2, and run 'gconf-editor'
• Navigate to desktop->gnome->peripherals
• Ensure that peripherals->touchpad:touchpad is enabled.
• Ensure that peripherals->bcm5974:disable_while_other_device_exists is disabled. 'bcm5974' is probably specific to my MacBook Pro's hardware, so you may need to search around for variable disable_while_other_device_exists under the entries listed under peripherals.

HTH