In 2009, scientists at Queen’s University, Belfast published the results of a study on paw preference in cats. When cats are playing with a fishing-rod toy, the scientists found that they were equally likely to use either left or right paw, but when posed with the more complex task of getting food from a glass jar, male cats were found to show a strong preference for using their left paw, while females used their right.

In humans, left-handedness has been associated with the hormone testosterone (which has been used to explain why more men than women are left-handed). Exposure to testosterone has also been shown to result in a female cat changing her paw preference from right to left. Scientists do not yet know why the hormone has this effect, or whether it is testosterone that is responsible for the initial handedness.
From: William Hartston; The Things that Nobody Knows: 501 Mysteries of Life, the Universe and Everything