This is very cool for everybody. AirPlay, which is basically the new name for AirTunes, but with a lot more going on, will be open to third-parties.
That means that rather than the format being closed to Apple devices (i.e. MacBook Pro to Apple TV) manufacturers of other speaker systems will be able to use Apple's AirPlay format for their speakers:
AirPlay lets you stream music throughout your entire house ‚Äî wirelessly. AirPlay wireless technology will be fully integrated into speaker docks, AV receivers, and stereo systems from companies such as Bowers & Wilkins and Denon. So you can enjoy your entire iTunes library ‚Äî every song and every playlist ‚Äî wirelessly.
We just hope that devices that incorporate the receivers will be made fairly inexpensive. For some reason we can imagine having a set of speakers in each room of the home and being able to listen to your music or Podcasts no matter where you around the house.