Well, it turns out not fast enough!  Years ago, in addition to a traditional starters pistol, Olympic officials started placing loudspeakers behind the athletes so that the sound would reach each athlete at the same time.  It turned out however that the athletes would continue to wait for the sound from the actual starters pistol to arrive.  Even with the loudspeakers, the speed of sound was still slowing down the athletes furthest from the starter pistol.  While we are talking about tiny fractions of a second, with Olympic runners and swimmers, it really makes a difference.  Starting at the Vancouver winter games and this summer in London, they are using a silent pistol that is completely electronic and generates a beep from the loudspeakers only (although it does make a flash).

[via The Atlantic,  dailymail.co.uk]