I'm probably very late to this party but that doesn't mean I can't enjoy it as much as everybody else.
Having ripped all my CDs and put the originals into storage (well, the loft), it means I need only my amplifier and iPod base station to access my entire music library in the living room. Wouldn't it be good, I thought, if I could choose tracks on iTunes on my laptop and get the sound to come out of the stereo. It would be so much easier than having to get out of my seat every time I wanted to change playlist. My mind leapt to thoughts of trailing wires, laptops that were suddenly somewhat less mobile and several broken ankles.
Mercifully, Apple have a solution: AirPort Express (and Extreme if you have more money than sense). It does lots of other cool stuff but the main thing one would buy it for is its iTunes integration. Put simply, you plug it in, install the software on your computer and five minutes later you can wirelessly beam music from your computer to your stereo. How cool is that?!