It is true that reversible computers can solve the issue of necessarily losing heat due to entropy decreases, but current computers are still far too inefficient for entropy loss to be a concern.
As I see it, if you're transistors did not dissipate that energy as heat, and instead 'stashed' it so that it could be re-used. Then you're 4 Ghz CPU would no longer need a heat sink.
From Wikipedia:
> At 20 °C (room temperature, or 293.15 K), the Landauer limit represents an energy of approximately 0.0172 eV, or 2.75 zJ. Theoretically, room‑temperature computer memory operating at the Landauer limit could be changed at a rate of one billion bits per second with energy being converted to heat in the memory media at the rate of only 2.85 trillionths of a watt (that is, at a rate of only 2.85 pJ/s). Modern computers use millions of times as much energy.