Well, now that I've listened to some 256 kb songs, I think I can hear a certain level of difference. 128 kb being "unlistenable" is definitely a huge stretch for me (it's perfectly good for casual listening, and most of the time when I'm listening to music, I'm "casually listening"), but I agree that quality is a lot more important in classical (symphonic, orchestral, etc) music than in certain others. Any music that contains a lot of subtlety, really.