It may be of interest to some of you that tomorrow night on Discovery Channel there is a 2 hour documentary on the Science of Sex Appeal.
Female
Straight
26 (soon 27)
Guys usually comment on how laidback I am.
Male, hetero, mid-40s
A common thread in compliments I’ve received from women who were breaking up with me is that I’m exceedingly non-judgmental. This is the part of the post where I’d make a joke and call them whores, but it’s really perplexing. It apparently makes women feel very (emotionally) safe around me, but most of my friends agree that while it is indeed a good quality of mine, it’s not necessarily a quality that is doing me any good.
Male, hetero, 28
That I’m genuine, real, down to earth.
I hope it will pay off for you eventually, and that you don’t discard that good quality.
Female
Straight
30
My (emotional!) warmth. Both men and women comment on it, and on how approachable and easy to talk to I am.
Male
Straight
26
For people who get to know me and actually care, probably my ability to stay calm under pressure. Also for those who know me for a long time, I will see any task through to the end.
I don’t know if people are attracted to these traits though. People seem to like zany life of the party types in the career I am in.
Male
Straight
39
You know, I can’t remember ever having received a compliment about my personality. 
So I asked my wife just now about what she thought my good points were, and she said I was sincere and sweet. And now I remember that she’s told me that before. I guess I am, to her, but not to everyone.