Does Temperament Really Matter?

Everyone seems to be buzzing about the place of temperament of the candidates throughout the campaign. Senator McCain began coolly and calmly and was often level-headed, but has since began to let his feelings of frustration and anger show, especially in the debates. Senator Obama began with a bit more fire but has leveled out and remained steady and generally passive throughout the last few weeks of campaigning. But how will their temperaments affect their votes?
I feel that both candidates are very passionate about their beliefs and policies, and about the future of this country. However, the mud-slinging is starting to get out of hand. McCain's constant dirt-digging on Obama as well as the ever-present question of "Who is the real Barack Obama?" is starting to get a little old. We all know their voting histories and we've all watched them flip-flop (though not as much as poor John Kerry in 2004) and stretch their policies a little, but is their temperament really that big of a factor?
Yes, it would be quite unfortunate if McCain lost his temper in front of a gathering of heads of state, but his foreign policy experience is nothing to scoff at. And Obama maintains a cool and collected front at all times, but his passive front can't always cover a lack of experience. I think when it comes down to it, it should be the experience and policies of the candidates that should determine the outcome of the election. After all, doesn't everyone get a little hostile during a heated competition?