Arkansas is very nearly the last state Obama would waste time in. So to summarize with brutal candor: Obama's biggest political problem nationally is with white rural voters and that only so happens to be the very group that decides races in Arkansas.
As John noted, these voters have a old, white fart to vote for. Actually, McCain's social and economic politics fits better with Arkansans than does Obama's. Obama is noted for being one of the most extreme socialist, liberal in Congress. Then there is Obama's anti-Americanism. People in Arkansas still honor the flag and our service men. You can be sure Arkansans noted his ditching the wounded at Landstuhl. McCain has been visiting Arkansas because he knows that he's going to get a good reception. There is a point I disagree with John.
A postscript: If Obama carries Arkansas, it'll mean there's one seriously massive national landslide for him. Which there could be.
There's a chance Obama could win, but it won't be a landslide. It'll be very close.