I just installed Ubuntu Intrepid on a paid of new nvidia-based Mac Minis (March 2009 model). Neither one has working sound. I've walked through the entirety of http://help.ubuntu.com/community/SoundTroubleshooting and tried everything on there short of recompiling ALSA from source. Plan to try that next, but if that fixes it, then you guys still need a bug report because the distributed build will need to be fixed, too. :)
Another thing that confuses me is that the troubleshooting tips on that page all seem to refer to ALSA for everything, while Intrepid appears to use PulseAudio instead. The only device that shows up in alsamixergui is PulseAudio. I did try uninstalling pulseaudio and just using bare ALSA, but that didn't change anything. I also installed the PulseAudio Device Chooser, and the only device it lists is "Default".
Everything in the system seems to claim that sound is working, and it all goes through the motions. There's just no sound coming out of the speakers. I do get the boot chime, and sound works in OS X.
DistroRelease: Ubuntu 8.10
Package: linux-image-2.6.27-11-generic 2.6.27-11.27
ProcCmdLine: root=UUID=c7151270-9d7a-4a98-b29f-8e1722385315 ro quiet splash
ProcVersionSignature: Ubuntu 2.6.27-11.27-generic