UPDATE: The "alert" alias has landed in Maverick's /etc/skel/.bashrc ... thanks for your support!!!
How often do you run a command line tool on your desktop that takes a really long time? Maybe something like make, debuild, rsync, or wget?
You probably kick off the long running job, and then alt-tab over to something more captivating than watching gcc fill your scroll back buffer -- maybe your web browser or news reader.
You occasionally pop back over to your shell to check on your job. Maybe it's still running. But maybe it finished a while ago. Dang.
No need to beat yourself up over wasted cycles. You can tell your shell to ping you when it's done. Just add this alias to your ~/.bashrc.
alias alert='notify-send --urgency=low -i "$([ $? = 0 ] \
&& echo terminal || echo error)" "$(history|tail -n1| \
sed -e '\''s/^\s*[0-9]\+\s*//;s/[;&|]\s*alert$//'\'')"'
Install the notify-send utility, and source your new ~/.bashrc:
sudo apt-get install libnotify-bin
Now, run a long running job, and append "; alert" to the end of the command, like this:
sleep 20; alert
After running the target command, the alert alias will render a notify-osd pop-up on your desktop, telling you the command you just ran, and its exit code.