A linguistic professor once told me that accent discrimination is the only socially acceptable form of discrimination left--well, minus sexism, racism, classism, ageism, heterosexism, etc...but there is still something to be said about the tendency for people to judge others based on dialect, and for this to be acceptable.
Even aware of this tendency, I still slip up. A teacher's assistant for a political science class is from England, and just because he has that wonderful British intonation, I register him as more intelligent. Well, I don't always pay attention when people speak, and finally I decided to follow along--needless to say, the bloke is not quite my idea of intellect of the year. But I let the sound of his voice guide my perception.
Aside from being the perpetrator, I also can also fall victim to this tendency. You see, I am from the valley--as in valley girl--and while my "likes" are not abused, when I get very excited or am with good friends, that pitch infamous valley girl pitch kicks in. And let me tell you, I have been assumed to be stupid, ditsy and the like because of it.
So just a gentle reminder, it's not how people say it, but what they are saying. And, as always, a person is more than appearance and sounds.