There's an old tale that often surfaces around the time of presidential elections that the taller candidate has won every race since 1900. That's not entirely true, as this exhaustive Wikipedia page devoted to the topic details, but there is a tangible benefit to towering over your opponent: the taller guy has in fact won the popular vote 65 percent of the time.
The percentage is certainly high enough to give Republican candidate John McCain pause: a shrimpy 5'6," the septuagenarian is a solid half-foot shorter than his opponent, 6'1" Barack Obama. (At least he'll have momentum on his side: 5'11" George W. Bush defeated both the 6'4" John Kerry and the 6'1/2" Al Gore.)