Currently I have nzbdrone configured and running quite happily on a Linux machine. I have set Growl in nzbdrone up with the proper hostname, port and no password. I click on Test and nothing happens. Nothing shows up in the logs either. I can telnet to the growl port from the Linux machine to my iMac without a problem. Other notifications from other applications on the same Linux host work as well.
This one is already on Trello: https://trello.com/c/bgU2cqFm/521-growl-on-os-x-doesn-t-work
The implementation was against growl for windows, not sure if the two are compatible.