The composition created by Steve Jobs and John Mayer during the Macworld keynote while demoing GarageBand has been posted online. It’s an AAC (.m4a) file, so you’ll need iTunes or another .mp3 player that supports AAC-encoded audio to listen to it.
(via MacMinute)
iTunes: “Macworld SF 2004 GarageBand demo” by Jobs, Steve/Mayer, John (2004, 1:36).