Deep South or Old South?

Someone stumbled on my blog and emailed me this

One note: there is some debate as to whether South Carolina is "the deep south", "the old south", or both. More info:

As a native Georgian and former Charlestonian, I have always understood that the Deep South referred to the post-cotton-gin regions of the south -- where there are vast, seemingly endless plantations fields (Alabama, Mississippi, Louisianna, and Arkansas).

A good book on the subtle differences between "deep" and "new" and how they've affected modern life in the South's major cities is "New Men, New Cities, New South".

I thought it was interesting. As someone 'from off' (as they say around here), 'Deep South' was the only term I had encountered, and from what I had gathered, referred to mostly the southeastern US (why not the rest of the southern US, I could never figure out). I always thought it was just a geographical term, but Wikipedia's Deep South and Old South entries would imply a historical and cultural distinction between the two terms.

Maybe some of you local readers can help educate a foreigner :)