But there are other outstanding ones.

Fair enough -- I guess I've just never met, nor seen on TV, enough people from these rural accent pockets to have noticed them. Perhaps I'll amend my opinion to say that N'awlins is one of the US's very few distinctive urban accents.

And yeah, I think it's true the world over that people can distinguish much finer gradations of accent in their immediate locality than in other parts of the world. I knew southerners at university who claimed not to be able to tell the difference between Liverpool accents (think Yellow Submarine) and Manchester accents (think chief baddie in Gone In 60 Seconds), although to me they're as different as French and Australian accents.

Peter