Well, first, let me ramble on about my little beef with this. XD
... It started when I was testing one of my new maps, a magma chamber for one of my elemental characters, and thought: "Gee, if I could add some background music in - it would give the place the total ambiance I'm aiming for!" And so I tried incorporating the music file in with meshes, but that just blocked out all the cool sound-effects I had installed on other objects... And generally turned the coolness into herpderp. X.x
Since I'm a bit of an audiophile, and I know I'm not alone... It'd be kinda cool if we could somehow specify background music for custom maps, (and I say background music - so that there's that option to turn it off while still hearing the sound-effects of other objects/walking/swimming/etc.), it would add a whole new level to creating maps. ^.^