Actually, I've read somewhere that there's a difference between genetic perfect pitch and trained perfect pitch. Those with the first find it physically painful to hear off-key music and to transpose known music into different keys (because it jars so much with their memory of what it's supposed to sound like), while people with trained perfect pitch have more tolerance for those things because the association isn't as ingrained. Kind of like the difference between synaesthesia and learned colour-letter combinations I guess.