Sorry I'm relatively ignorant when it comes to these topics; what does this mean? What are you able to do, upon listening to a particular musical performance?
Most people have no (or very little) sense of absolute pitch - if you get asked to sing / hum / whistle a song, you'll start on any random old note. You'll get the relative pitches right - the change in pitch between notes - but not the absolute.
(To be pedantic, you'll get the ratio of the frequencies approximately right)
Someone with perfect pitch can identify "that note is the A# below middle C", for instance. But not necessarily that accurately. " not the greatest at determining tunings by ear " just means that he's not very good at it. So he may identify that A# as a C or something.
But it's honestly not that valuable a skill, even for professional musicians. Having really keen relative pitch (and avoiding slipping pitch if you're singing, for example) would be a much better focus to take.
I believe most (if not all) natural tonal languages use relative pitch, not absolute, so you wouldn't need perfect pitch to understand them.
I did turn up that a much larger percentage of people have perfect pitch in populations that speak tonal languages.
From http://en.wikipedia.org/wiki/Absolute_pitch "[...] there are no reported cases of an adult obtaining absolute pitch ability through musical training; adults who possess relative pitch, but who do not already have absolute pitch, can learn "pseudo-absolute pitch", and become able to identify notes in a way that superficially resembles absolute pitch. Moreover, training pseudo-absolute pitch requires considerable motivation, time, and effort, and learning is not retained without constant practice and reinforcement."
Studies have shown that there is a higher prevalence of people with perfect pitch in countries where tonal languages--languages in which the same series of sounds made with distinct voice pitches can denote entirely different words.
However, the percentage of people with perfect pitch remains tiny, which is not what I would expect if it was due to training alone. It seems like it might be helpful enough for musicians that we'd have turned it into a method by now if training alone reliably produced good results.
Hmm, it depends from listener to listener. Obviously I can't comment for your partner, but I too have perfect pitch. Bad alignment of players isn't really a problem for me unless the players are dramatically out of tune. I'm not the greatest at determining tunings by ear either, as this kind of thing varies.