I use an Infrant ReadyNAS at home. It actually supports AFP, performance blows the slug away, and it comes with mt-daapd preinstalled. Problems with it though, are 1) it’s relatively expensive; and 2) it uses an old version of mt-daapd. But it sounds like they’re testing a newer SVN FireFly version and it should be included in their release soon. Power consumption is more than the slug (which is why it’s faster), but it’s still much less than running another desktop (peak is ~75 watts with 4x750GB hard drives spinning).