wma, ogg, ac3, ra, liquid music, etc, etc, also all supposedly give more quality at a smaller size.
do you see any of THESE FORMATS on your friends' hard drives?
mp3 has had way too much publicity (in no small part to Napster) and therefore has way too much momentum. Not even the illegal anticompetitive tactics of a twice-convicted monopolist can dethrone mp3 at this point. (Although they are trying very very hard!)