I been told that spelling ability (good orthography) is correlated with intelligence (which is a nice way to say: if you are bad with orthography, you are stupid). So far I have been unable to find a conclusive evidence based answer
I found this link, that says there is a correlation between personality and orthography (if you are more confident, you are more likely to make mistakes).
And this article at the Straight Dope which says that if your spelling mistakes are from dyslexia you are not necessary stupid.
But neither of them answers my question. Is there a correlation with adult intelligence? (I do not believe so, because I have met smart people that are bad at spelling, but they might be an anomaly.) So I would really like to know if that is the way it works in the majority of the cases.