The degree to which it is offensive may vary, but of course it's a racist term.
BTW, Yesterday I saw a guy from Iowa driving a corned-up pickup truck. You know... corned-up... with a blown hemi, 10 extra fog lights, super lift kit, dual cab-mount air horns, playboy mudflaps, a gun rack, and "I'd rather step in sh*t than smoke it" bumper sticker. Those "corn-ers" really know how to dress a truck.