i have very sensitive ears; not quite up to perfect-pitch level i think [because i can't tell notes off by ear], but they're really sharp.
for example, let's say that somebody plays a note that is different from the note it should be according to the key signature, i.e. when F# is played when the key signature says it sould be F, just plain old F. however, no matter which natural+flat/sharp combination it happens to be, when something like that is played a wavy sound always comes up in the air. my ears can pick that up even when i am playing in my 60-piece/6-section concert band at school.
for me it's practically hell, having hearing like that, because i hear the "wave" as something very clear and very prominent. but for my bro, it doesn't bother him much because unless the note conflict is amplified by speakers or whatever he won't hear it as clearly; it just comes across to his brain as a slight disturbance, whereas for me it's like thunder.
[i guess you could say that's one disadvantage to having that kind of hearing, heh.]