How do you figure most don't know what it is? A lot of folks use the AIM space to write a goal of theirs instead of listing a messenger username. It's kind of a trend.
just because people put something other that their AIM screen name on their profile doesn't mean they don't know what it is, I did not put my AIM screen name on my profile because i don't want random people IMing me
I think that most people know what AIM is. But it really isn't that popular these days, so people use that part of their profile here to put silly things in.