Brad Pitt is, of course, from Springfield, MO, so he ought to have an Ozarkesque accent (Southern), a la Harry Truman, but as I remember, a lot of folks in Jacksonville, FL (aside from old timers) don’t have that much of an accent. Eastern TN natives should have a fairly distinctive Southern accent (especially if from the rural, isolated areas - such as Dolly Parton, and probably not terribly far removed from Loretta Lynn, from isolated Eastern KY). Of course, I’m a Middle TN/Nashville native, but I don’t sound like I’m from here at all, I sound Yankee to Southerners and Southern to Yankees. No one has ever correctly guessed my state of origin upon hearing me talk.
Anyway, I hope I get to see IB before long, most likely on DVD where I can control the volume, unlike in the theatre. :-P
A lot of actors learn to use different accents. That is why they have “voice coach” positions.
In the more blue collar neighborhoods of the Jacksonville area, you will still find some folks who speak with the classic Florida Cracker accent, ("Floorida"), but it has been dying there for some time. I still don't understand why me BIL (who was raised in North Palm Beach to parents from New Jersey and Connecticut) has a slight cracker accent, even though almost everyone else there does not. When I heard Pitt speak, I thought he sounded like a more rustic version of my brother in law.