Recently I discovered an oddity which I thought was worth mentioning in this forum... I selected an .mp3 on the desktop file and did a Get Info (Command-I). In the Preview pane, I clicked on the Play button, and the file started playing. For some reason, when activated fast user switching to change accounts, the audiofile kept playing. I even logged in as another user and still the music was playing.
Not very useful, but nevertheless......
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040225113100140