I have just added one of these to my vintage(ish) home stereo setup, and I'm freakin' thrilled
The AirPort Express gives me a wireless feed from the iTunes library on my computer (on the opposite side of the room from my stereo rig), and allows me to control songs and volume remotely from my iPod Touch. Adding an additional AirPort Express connected to another set of speakers will allow me to stream the same music to those speakers and control their volume independently or simultaneously.
My wife and I throw quite a few large parties during the year, and being able to have the same music playing throughout the house and outside while having total control from my iPod is a perfect setup for me.
