I am a transplant from Ohio to here in South Alabama, and I have never encountered any hostility because of being a northerner. I have taken some good-natured ribbing, and have been told I have a "cute accent", but have never been subjected to any hatred. This is just my personal experience, and I don't disbelieve others who have different stories.
That said, I just wonder if some Yankees bring it upon themselves with a snarky, demeaning, superior attitude towards southern people and southern culture. People can sense when they are being belittled or looked down upon, and I think a lot of people from the north have a prejudice about southern folks. I agree with the poster above who states that southern culture takes some getting used to, but I for one have come to appreciate so much about it. And, I will defend my Alabama friends against anyone who tries to define them as ignorant, "redneck", backwards, or any of the other nasty things I have heard people up north say.
Respect is a two-way street.