After trying to make GNOME and KDE work as my GUI, I have settled on XFCE. But, one annoyance was that I would lose audio if I used the Apple keyboard mute keyboard key and not be able to get it back until after a reboot. Also, when it was working, it was horrible quality. I tried many workarounds but this fix finally did it. This is on Ubuntu 12.10 64bit, so YMMV. The problem is in the fighting between alsa and pulse audio under linux.
1. Purge your alsa installs and configs
$ sudo apt-get purge linux-sound-base alsa-base alsa-utils
2. Reinstall them
$ sudo apt-get install linux-sound-base alsa-base alsa-utils
3. Make sure you have all the xubuntu XFCE goodies (maybe not necessary, but I messed around so much, just a CYA)
$ sudo apt-get install xubuntu-desktop
4. Then purge pulseaudio to stop the battling.
$ sudo apt-get purge pulseaudio
This worked for me to now allow the Apple Mute or F10 key to toggle sound off and on. Prior to this, the mute toggle key (F10 on the Macbook Pro) toggle-off would work, but it would mute both alsa and pulse systems under Linux. The increase volume (F11) or the F10 key again would not kick it loose and it would stay muted until a power cycle. Essentially, it seemed XFCE wasn’t passing the proper command to the pulse audio mute.
After this, I am able to use the keys. Anyway, it sort of issue would probably come up on other laptops with media keys as well.