It depends on the where you are from in America. Generally being from the west coast i don't hear that greeting much.

Yes, particularly in the South and West.

In the old warner brother's cartoons there was a character who would say 'howdy partner'. I think it was....I don't remember but he had a big mustache and carried one or two big revolvers. It was his catchphrase.

We'd say it in England but we'd be referencing American films, probably old cowboy ones.