This was a spontaneous answer to a question I've received.
I thought it's good time to talk about licensing of software and creative works.
I talk about free and open source software, and free culture and what do you need to know about licenses if you want to sell your music.
I forgot to mention the BSD license as one of the more liberal ones (probably a bit similar to MIT). GPL being a bit limiting in the regard you can't appropriate any software that it touches, unlike with the other two licenses.
Enjoy!