[jesse9766]

Latency is an issue even inside a transistor itself, something known as propagation delay. When you have a bunch of logic gates chained together the propagation delay increases and the chance for a race condition occurring also increases. The propagation delay of a logic gate is one of the limiting factors of the speed of a circuit.

Transistor gates act as capacitors in a way. This capacitance increases the delay between switching on/off. [1]

To lower this delay, we can shorten the transistor gate. We've hit a wall with how small we can shorten this length, and it is exceedingly difficult to make smaller gates without running into quantum effects.

Higher electron mobility means that the delay inside the gate is reduced, allowing faster circuits.

[1]http://ece-research.unm.edu/jimp/vlsi/slides/chap4_1.html Switching speed of MOS systems strongly dependent [on]: Parasitic capacitances associated with the MOS transistor. Interconnect capacitance of "wires". Resistance of transistors and wires.