Probably the part that makes sure that voltage and power levels are stable before enabling the rest of the CPU. That might sound somewhat cheeky, but it's true! (It's called a power supervisor circuit)
EDIT: The part about receiving the foremost electron is somewhat nonsensical since it's not like in a water pipe where one molecule of water makes its way through the pipe. You establish the electric field first (propagates outwards first) and then electrons jostle themselves around in a fashion not unlike a Newton's cradle: http://en.wikipedia.org/wiki/Newton's_cradle
So the current starts up everywhere once the field is established. As for how the field propagates, well that goes along the length of the wire at some velocity a little less than the speed of light.