Professional musicians probably do this all the time, annotate their music and then use software to have it played back. The idea hit me when I was wondering how I could go about listening to the new Beck album, all written on sheets. I can't read music so I wondered if there was a software for it, though the software doesn't quite do what I would like to do.
Folks like Garageband and http://www.finalemusic.com/notepad/ will play your music if you type it into their software, and it will then play it back if you own the right software. Obviously, this is very useful for a professional musician, in effect they can demo their work as they write it without having to stop what they're doing.
But what about the amateur? What if you wanna look and listen to say Mahler? If you are a dilettante or a rock critic, what can you do. Maybe you just wanna see how the music looks while you're listening to it? I dunno if this will do it and I absolutely don't know if it sexy enough to get out of the world of the pros to the layman.
The flipside is, changing your recording into sheet music… now that's a cool idea and you can do it. All you have to do is convert your music into Midi Files and whomp here it is: http://www.notation.com/NotationMusician.php . But again, how do you really really sell this out of the world of professionals. And why would, say, Kelly Montoya want her songs on sheet music? I mean besides the wow that is cool vibe?
Given the right spin, the back and forward between sheet music and sound via software could be seen as something awful fun. If you were to pick up your guitar, write some lousy song, and then be able to change it to sheet music with your name on it, you could be the next great composer…. or at least feel like it!