I've got a final revision of the G4 Mac mini, the 1.5GHz model, dual booting 10.04 LTS and OS X. One of the issues I've had is that the internal speaker doesn't work under Linux, or so it's been reported on various post and sites. It turns out it's a simple matter of flipping some ALSA control options. With an ALSA mixer you must enable both the Speaker and the Headphone to get audio to play over the internal speaker. It will still play over the external headphones/speakers if they are still plugged in. I'm not sure if this is a problem with the ALSA, OSS, PCM or snd_powermac drivers or just something setup wonky in the configs. I've used both GNOME ALSA Mixer GUI and the alsamixer command line tool to do this. The alsamixer tool will mostly work in an X-term, as the F-keys don't pass though. It is fully functional on a console login. I also noticed that audio plays back per-user. When I switch from X to a console he sound is cut off, and when I get logged in as the same user the audio comes right back in.