I think it does exist, but there is also a huge set of hidden social rules. Often the southern habit of a smile and easy going demeanor masks something less than 'nice'.
It honestly just depends on where you are in the south. If you're in a large southern city (Memphis, Atlanta, etc.) there probably won't be much. If you go to smaller cities or towns and get to know the people it's totally clear that southern hospitality is NOT a myth!