I came across a comment about a small but useful utility I had not heard of before called Unplugged. This utility (in the form of a System Preferences panel) from Briksoftware watches for events related to your power cord being plugged or unplugged and notifies you via Growl (if Growl is not installed, the application will use an alert window).
You can choose whether it starts on login, whether you are given an extra notification when battery resources are at a level you define and can restrict display if designated applications are currently running:
You also have complete control over the information presented in the alerts:
With my Growl configuration, the notifications look like this:
It’s a very simple application that does not require a substantial amount of system resources (as shown below). There have been times when I have had the MacBook Pro become unplugged and not noticed the screen dim only to discover much later that I’m on 50% battery left. This utility would have definitely come in handy then and is now a part of my “must have” applications.
I had a bit of trouble trying to send a PayPal donation to the author via the link on the page, but managed to do so via the standard PayPal “Send Money” option. As always, I highly encourage folks to support independent development on the Mac.
If you use Unplugged or have suggestions for other small-but-useful utilities, drop a note in the comments.