I played around with an old Mac Mini as a music server for a while, but the one I had could not run modern iTunes, so sharing with other devices in the house proved difficult.
I then went back to an old P4. When that motherboard died, I went out and bought a netbook running W7 with 2GB of RAM. It runs Logitech Media Software, and I use a usb-spdif converter into my Pioneer receiver. I control it with a gen 3 iTouch.
Works great, and for the $200 I spent for the netbook, I am very happy with it.
I do know that folks using DSD report great things about the CAPS pieces, but for my collection (1TB of FLAC with a bit of 24/96 and some WAV thrown in) the value of the netbook is perfect.