Apple's small wireless device is a neat package - connected to the internet it can distribute to ten devices (computers, Apple TV, iPhone, etc.), can allow all users to access one printer and can allow your iTunes music to be distributed wirelessly to one or more powered speaker systems around the house. It can also be an add-on to a larger network.
But there is more! When on the road it makes a very useful wireless hub for computer and iPhone, whether in the hotel or the office environment, or both. The device is small and light and has no need for power cords as it can plug directly into a wall socket or power strip.
Although I haven't done this yet, it is clear that the combination of iTunes, Airport Express, power speakers and iPhone with the Remote app makes for one very sophisticated music system. To whit. Computer is in den. Speakers are in living room. iPhone can adjust the music selection and volume from anywhere in range of the wi-fi network, say the kitchen! Moving from living room to dining room? Simply switch to a different set of power speakers (though this requires a second Airport Express).
This is all very impressive and speaks volumes for Apple's commitment to controlling all aspects of the system, from computer to OS, to software, to peripherals.