Growl is a “global notification system” for OS X. Applications can use the Growl framework to display notifications to the user. I use Growl with Adium, and it works wonderfully.
The Growl package (download) includes a utility called growlnotify, which can be used to display notifications using the command-line. I use the following bash script (growlexec) to run a specified command and display a notification when done:
#!/bin/bash
$*
if [ $? -eq 0 ]
then /usr/local/bin/growlnotify -m "\"$*\" done (SUCCESS)"
else /usr/local/bin/growlnotify -m "\"$*\" done (FAILED)"
fi
Here is a screen-shot of growlexec causing a Growl notification to be displayed after a successful nmap run:



I don't get it
I've never had a need for anything like this. How often do you use it? Do you actually use it to notify you when nmap completes?!
I don't get it
Yes, sometimes nmap takes a while to complete if it is a remote host and I'm scanning all possible ports.