Your life is not complete with out one
I'm slowly getting the Apple addiction, started with an iphone, now got one of these. Think a Macbook is on the way next. The airport allows you to plug all sorts of stuff into this cool looking little box which hangs off a 3 pin electricity socket. You can play your music on your hi-fi (if its plugged into the little box) wirelessly from your laptop over wifi, it will also support a USB printer, and an internet connection if you plug it into your router. You can also (apparently - just about to install it and try it) use your iphone or touch as a remote control, allowing you to play any track in your collection from pretty much anywhere in your house or adjust the volume.
Edit: just set up my iphone as a remote control using the "remote" app. Its amazing. You can even switch between different speakers using it.