The southern accent was a little off, but all in all this was a pretty virtuoso performance.
It seems that Miss Walker has nearly ten million views on Youtube. This video of hers suggests that she can do a better southern accent - certainly much better than I. She has a number of what seem pretty interesting videos posted there.
And this is a short but sweet excerpt from Robin McNeil's "The Story Of English" describing the major American accents:
Even though I grew up in Maine, my parents were from the midwest, and so I sound very strongly Midland. And this young man is pretty talented, offering 24 different English dialects. The dialog is NSFW, but I love the space alien reference in the Welsh accent. Very UK inside baseball. Or cricket. Or something.