Pitching hitting: Helping their own cause
The posterboy for a pitcher being able to handle the bat is Arizona's Micah Owings. He is probably known for his hitting ability as much as his pitching ability. The St. Louis Cardinals' Rick Ankiel also has a feel for hitting the ball, though he is strictly a position player these days and it is almost too painful to learn how he got to be where is he as the Cardinals' starting center fielder.
Over the years, a pitcher hitting or a pitcher doing a 'non-hitter' thing have been captured on various cards. Unless they were two-way players at some point of their baseball lives, I think a lot of pitchers' hitting ability to swat a baseball has to do with luck, since it isn't their main focus. They have to do the little things, like be able to get the bunt down and move the runner over, but it isn't like you would pay to watch pitchers hit during BP as a whole.
Not even Greg Maddux and Tom Glavine's best efforts will take attention away from those who hit long balls for a living. Even if these hitters' home run numbers are riddled with mental asterisks.