The following is an overly simple example, and source:
focus the browser on the correct element (click on it, or tab to it) up, up, down, down, left, right, left, right, b, a if you've typed the code in correctly, you should discover the Easter egg. :) NOTE: like the original, you've got to be quick or else the code won't work.
And this example is more how I envisioned this guy getting used - in some random web app, as a private joke for the developers and a few insiders. Clearly this second sample is fake, but I think it gets the point across.
Postscript: (01/12/08) - if the sample doesn't work for you, from the guy who wrote the Scriptaculous sound engine:
If you have a Mac, you're all set. QuickTime takes care of all browsers. If you have IE, you're also set. bgsound is a wonderful thing - wav w/ no plug-in. Opera? Terrific. Wav files with no plug-in. FF on the PC? Only if you have QT installed. Otherwise you hear nothing. For now.
These details are provided for information only. No information here is legal advice and should not be used as such.