September 17, 2007: More info on launch delay
It seems that the EMC puts the car in neutral when I come to a stop with my foot on the brake. When the light changes, I take my foot off the brake and gas it - producing a 1-2 second lag before accelerating, because the car is in neutral and the computer has to tell the transmission to engage the gears. (This is not noticable in "normal" driving in either standard or sport modes).
The way around this is to stop the same way, and when you have come to a stop, pull on the handbrake and take your foot OFF the brake pedal. When the light changes, release the handbrake and gas it - resulting in instant acceleration, no lag, just go.