Apple's new AirPort Express and AirTunes (available next month) are a pretty slick combination. Other companies have made it possible to play MP3s and other audio files from your computer to stereo systems in your house, but this is the easiest-looking setup yet.
The only disadvantage? You still have to run the music selection from your computer, instead of at your stereo.
Oh, and here's a good point:
In the hands of a typical user, a six-month-old Mac is almost certainly in similar working condition as when it left the store; a six-month-old Windows PC, on the other hand, is likely to be infested with multiple instances of crapware. And if it's not, it's likely because the poor sap who bought it just got done reinstalling from scratch.
All the computers at our house are behind a digital firewall, yet I still have to be extra-vigilant with the Windows boxes about various sorts of viruses, Trojan horses, and other (as Gruber puts it) "crapware."