If you want to release your music for everybody to hear then it's a good idea to licence it with a creative commons licence. That way your music or drawings can be remixed and used in surprising ways.
But the emphasis on the finished product doesn't interest me as much. I'd rather open source the process by which art is made rather than the result.
The new wave of digitally assembled music opens the way to truly open source music - when music can have source code, can have a version history - we can all learn from how it gets made.
Put your music in the public domain if you like, but don't forget to release the things you learned along the way.