In spanish, I have noticed that people from Mexico say, if you are born in the states as "Ah, eres Americana". But I wouldn't say, "Soy Americana" if for example I don't have blue eyes or blonde hair. Unfortunately many people relate one with the other. Gringa = Americana
If I was "Mexican-American", I wouldn't say, "Soy Americana", I would say "soy ciudadana americana" or "nací en los Estados Unidos". Of course, this would only come up in some other country and not here in the U.S. (I don't think).
My co-worker who is also an interpreter is always asked what part of Mexico she is from and she very politely says, "soy de los Estados Unidos". She too, would not say she is "Americana" as she does not have the features of a "white person".
I agree with Rusty about the usage of the noun, unfortunately it is widely misunderstood.
