I've always been the most a-musical (and not in an amusing way) person I know. Last fall, I started singing lessons -- what a joy -- I LOVE it! Although I was VERY pitch-ignorant at first, I've been improving considerably (just sang a solo at a student recital a few weeks ago).

My instructor has said there are 2 kinds of perfect pitch - absolute pitch (where someone can sing any particular note on demand, or can name any particular note s/he hears -- it's all about labelling), and relative pitch (more common -- once you're given a note, you can move up or down from it with ease -- I think). She said she had read studies indicating that perfect pitch is developed between the ages of 2 and 5; once that window is missed, the note-sound-label connection won't be made. And, as Wordwind pointed out, perfect pitch does not necessarily make you a better singer.

oops - just saw Wordwind's last line. Should have read more carefully - could've avoided redundancy.