Have you turned it on?

I was about to post a blog following up on my Ubuntu Hardy Heron installation, bemoaning the fact that all of a sudden my audio stopped working. I had played with all the settings in System->Preferences->Sound, plus adjusted everything I could think of in the Volume Control. Nothing, nada, not a squeak.

Naively I thought it must something to with the installation. And then I remembered the physical mute button on the laptop itself. Whoops.