It doesn't play nice with pulseaudio we have xfce4-pulseaudio-plugin that works much better
using this one, didn't know another one existed
I don't remember how my system was put together back in Fedora 18, but among the function keys of my keyboard the audio ones never worked. That is, until I gave a try to xfce4-pulseaudio-plugin, so for this reason alone I'm now ditching PNMixer :)
PNMixer was probably here by default or ended up in my panel by accident, and it's a lot more beautiful (subjective opinion of course) but my desktop experience just improved by switching plugins. Thanks for even asking about that other one I never heard of and isn't even on my system.
Cheers