Well, the New York Yankees just drafted an ambidextrous pitcher - Pat Venditte Jr. Venditte was drafted in the 20th round of the 2008 draft and according to Wikipedia (he has a page all to himself):
When using his right arm, Venditte delivers over the top and can throw a curveball as well as a fastball reaching up to 91 mph. His left-handed delivery is side-armed in which he throws a slider and a relat ively slower fastball. Venditte uses a custom made six-fingered glove with a thumb-hole on each side allowing him to easily switch back and forth. He generally pitches with his right arm against right-handed batters and left-handed against left-handed batters which minimizes his opponent's advantage when strategically ordering batters in the line-up based on which side of the plate they hit from. Furthermore, by splitting his pitches between his arms, he is able to pitch longer than traditional pitchers before becoming fatigue.Here is the photographic proof from Chris Machian for The New York Times:
Here's his specially modified baseball glove:
Umpires working Creighton’s games have to dust off seldom-used rules regarding switch-pitchers. Like everyone else, Venditte gets only eight warm-up pitches upon entering a game and five before any inning, whether he chooses to throw left-handed or right-handed, and may not warm up again if he changes arms midinning.
A switch-pitcher facing a switch-hitter could make a fine Abbott and Costello routine. Against Nebraska last year, a switch-hitter came to the plate right-handed, prompting Venditte to switch to his right arm, which caused the batter to move to the left-hand batter’s box, with Venditte switching his arm again. Umpires ultimately restored order, applying the rule (the same as that in the majors) that a pitcher must declare which arm he will use before throwing his first pitch and cannot change before the at-bat ends.