Faldage, you bring up the point I've been thinking about all day: the distinction between the two given the fact that their definitions are identical.
I don't use honestness--at least, until today. In fact, when I first saw honestness in a word list, I thought, "That's one I'd have to check to make sure it's legit."
Anyway, now that I realize there are those who are using it, I've wondered about distinctions between the two--and wonder whether honesty is more active than honestness and that honestness is more of a mind set--or a state of heart or intent. Honesty is the attribute after-the-fact of doing--and honestness is more of... Oh, blarney! And I say that in all blarnestness.