Another disadvantage to having perfect pitch . . .
When I was in college I took a Early Music Ensemble class (medeival and Rennaissance choral music). A couple of the people in the class had what I'd call perfect pitch -- the ability to sing or identify a note on demand. Problem was, there were a few occasions when we needed to transpose a piece to a higher key (the basses couldn't get the low notes) and the perfect pitchers could not make the adjustment -- look at the sheet music, pretend the first note was a pitch or two higher and carry on. I think they had to actually rewrite the music in the new key in order to sing it.
I found that kind of funny since I really couldn't read vocal music -- I just kind of learned the pieces through repetition. And here were these hot-shot vocalists who could sing like angels, but only so long as they had the music in front of them. I don't think they went to song circles. :)
B.