It's purchase was brought on by the lousy on-board sound of my work PC. Even when there was nothing playing there was an annoying buzz that came through the headphones. You could change the pitch of the buzz by dragging windows about on screen but the novelty of this soon wore off.
Now I can listen to quieter music without having the annoying buzz intruding. It also just sounds a lot better generally.
I will also be able to plug it into my Powerbook and it has a optical digital output that I can plug direct into my amp at home.