I accidentally discovered a new feature in the latest update of iTunes. It seems, Apple has finally given us the ability to stream iTunes to more than just one Airport Express. I only own 1 express but there appears to be the option to select more than one. In the AirTunes panel, I already have 'Multiple Speakers' selected. My iTunes is simultaneously playing through my Powerbook speakers as well as my Express. For those of you with more than one Express, get cracking and see what happens.