How can I record the sound output with gtk-recordmydesktop?

I managed to get it going with the steps on the Ubuntu Forums, for clarity here is what I did:

1. sudo apt-get install gtk-recordmydesktop pavucontrol
2. Opened the Pulse Audio Volume Control dialog: Applications > Sound & Video > PulseAudio Volume Control
3. Opened gtk-recordmydesktop
4. In gtk-rmd advanced preferences, "Sound" tab, set "Device" to pulse
5. In gtk-rmd start a recording
6. In Volume Control goto the Recording tab and change the recordmydesktop entry to 'Monitor of '

This is what seems to have worked for me.

All I had to do was change DEFAULT to pulse in by: Advanced button > Sound tab > Device:.

If you use Pulseaudio, there is a howto in the Ubuntu Wiki. It basically boils down to using the pulse audio mixer, to re-route the sound from its source to audacity where it is saved instead of the default output (which would be you speakers).