Psychologists are far from a consensus on how to measure vague concepts like creativity and intelligence. Any declared correlation between those attributes and handedness will have to wait on a better understanding of the notions themselves.
So raise an eyebrow (right or left) at any labcoat making sweeping statements about the smarts of a potentially arbitrary 10 percent of the world's population. However, a few earnest studies have proposed interesting links between primary hand and cognitive skills.
It appears that righties may perform slightly better academically than lefties. Research also suggests that left-handers more often suffer learning disabilities and dyslexia. On the other hand, southpaws dominate in tasks involving the mental manipulation of objects, which might explain the high proportion of left-handed chess players. More general claims, especially concerning "right-brained" versus "left-brained" people, are more pseudo- than science. The only clear advantage lefties enjoy is on a baseball diamond.