Brad does a good job of explaining the gotchas to get everything working and then he does another article to show how to simply extend the idea with other styles of notification here.
If you don’t know what growl or in this case dgrowl are – they are a style of notification that uses dojo to put messages on screen either for a timed duration or as “sticky” messages to be acknowledged in your xpages app. What I liked about it was the simplicity of extending the approach and the relatively rapid setup (if you allow an hour you should be fine). I especially like the hierarchy of messages so that errors are at the top
To see the approach in use go to Brad’s demo page here and see all the examples (and other goodies too)