I have never had the need to go running around with guns shooting people, but paintball is something I play quite abit of. Not with semiauto and 8 million rounds ewither. Pump pistols, 10 shots, and 2 4man teams kicking the crap out of each other.
To tell you the truth I did not see much diff. in my aiming while running, still a crack shot. But when I had to dodge shit; trees paintballs, etc.; and when I was jumping or dropping from rocks and such, your aiming turns to total crap, I mean, I would be aiming at someone and he would have to run to the left 10 yards and jump 15 feet to get hit.
What would be really cool would be that the aiming while running would be less accurate, but not by much; BUT, while jumping it would become wildly erratic, giving you a better chance of pulling a muscle, then of actually hitting your target.