I have coworker who came up to me today frustrated.  His touchpad no longer worked and he couldn't figure out why.  He tried tweaking everything in the mouse panel, logging out, logging in, upgrading and downgrading packages, etc.

After some investigation, I determined he had accidentally hit fn-f8 instead of fn-f7 when trying to update his monitor configuration.  This is the "toggle touchpad" key, which he never noticed before.

It would be good if we somehow indicated in the touchpad panel that it is disabled (and potentially, but not necessarily add a way to re-enable it from the panel)