Well, I have to be attracted to his overall face and body first. I don't think I necessarily notice shoulder width on a guy, but I do notice if he has muscular shoulders/back. I'm not sure if that answered your question or not lol.
wide shoulders are so hot, they make me feel like he is going to protect me, but a lot of girls to me don't notice that, i always talk about wide shouldered guys, but then my friends are crazed over this tiny little thing of a guy. beats me. to me they matter, but not to all girls.
I personally don't have an opinion. I think both wider and narrower guys can be equally attractive. In history, however, larger men are more successful with women because larger men make women feel secure and protected. I honestly don't know anyone who notices or cares about how a man's shoulders are.