I was interested to read that some people think you must have perfect or absolute pitch in order to sing. I think it's quite the opposite. In my choir, I find the people with absolute pitch have the most trouble sight-reading and performing with the other singers. Why? Because my choir, like most, doesn't always stay perfectly in tune, and it doesn't always sing at 440. Generally, if the choir goes a few cents flat in performance it's not a problem, as long as all the singers go together. But when you've got some people with absolute pitch, this sort of fluctuation is extremely difficult for them, and they either try to stay "in tune" which jars horribly with the rest of the choir, or find themselves unable to sing much of anything at all.