I am not a birther, but the way he pronounces certain words convinces me that English is not his first language. Take for example his pronunciation of Corps as corpse. Or when he recited Psalm 46 and pronounced the bow weapon which is pronounced with a long O, the way he pronounced it means bending at the waist.
Personally, I have trouble listening to his affected Chicago accent, especially when he says words like 'jobs'.
Watch The Blues Brothers movie and listed to Dan Akroyd's character Elwood. To me, obama sounds like he's imitating Elwood Blue's' accent.