my ability to know songs that I've only half heard once before
Eh, most songs are the same songs over and over, so it's not that hard. I sing along with stuff and finish it and people go "wow did you know that" and I just think, no it's the only place that song can go (just like it's the place that song went the other 35,973 times someone wrote it.)
A really good friend of mine in the industry says "Good bands have one good song, great bands have two." And he's right about that far more often than he is wrong.