A few years ago I got into an online argument with a southern blogger (conservative) because I said Bush's accent made him sound even dumber than I think he is. But the interesting thing is, even with my natural prejudice as more-or-less a northerner (technically Maryland is south of the Mason-Dixon but we don't act it) it's not just that I automatically think southern accent = dumb, most of the time. For instance Al Gore, Bill Clinton and Jimmy Carter all have southern accents but don't sound like the local yokel. Even on the Republican side Mike Huckabee and Fred Thompson, while they may say really stupid things, don't sound like they're idiots.
Hell, one of my favorite tv shows of all time is all southerners and they come across like Ivy leaguers compared to Bushie.