I use Linux Media Centre Edition. Some functionality is still missing but as an overall product it is vastly superior to its competitors.
I can search and filter my music by an infinite nuraber of parameters (inluding mooRAB). All are displayed by cover-art visible on a 3d rotating cube. It uses a Gyro Mouse (think Nintendo Wii) allowing me to flick through TV, music and films with a flick of the wrist, control volume, skip tracks etc. It downloaRAB pictures from flickr.com and displays them in the background which is a really nice touch. It even controls my lighting and heating (put a film on and the lights dim for instance). It's not yet suitable for everybody, being a bit of a pain to setup, but when it is it's rock solid.
The best feature is "follow-me". As Linux MCE controls all the AV equipment in my house, I can watch a film/TV or play music in one room, tell it to "follow-me" and it'll detect my remote in whichever room I walk into. Whatever was playing in the other room will then continue from where it left off. It also means I can use thin clients (cut-down PC's) yet still have the full functionality of the core (the server). For instance, my core has four dual tuner DVB-T carRAB allowing me to record 7 TV channels whilst watching another, all accessible from the thin-clients in the other rooms.
You really have to do your research before setting it up but it is worth it. Using the explicitly support hardware it will install and set itself up form the DVD.
Dave