After I updated dbus, avahi and netatalk on my plug to the most recent versions, the afp service was no longer being advertised to my mountain lion mac. I was able to fix this by following step 5 of this website:
http://kremalicious.com/ubuntu-as-mac-f ... ne-volume/I was always able to log in to my plug via the finder's 'go' 'connect to server' option and inputing the right local ip address, but it was not advertised as available in finder.
For whatever reason, by configuring the afpd.service in /etc/avahi/services/ folder and restarting avahi, it now works perfect in ML.