Power/Watt improves, but manufacturers will push to maximise the amount of power they can put into a box before cooling it becomes a problem. The fun thing is that new hardware can be extremely efficient at doing things that are a few years old, for example: the chip on my Galaxy Nexus is good enough to play GTA3 and it doesn't take more than 2W.
The cool thing is that in a decade or so you'll probably be able to play PS4 quality games on a handheld (in fact you can already play 360/PS3 quality games on tablets).
This is becoming particularly interesting with desktop computing as the power requirements for average users has plateaued (most people just browse and email). So excluding gamers, people should find that a new computer will draw significantly less power than one built even 3 years ago. With Nvidia's Maxwell architecture and the upcoming push for 20nm things get a lot more interesting. The 750Ti draws 60W under load and can play plenty of otherwise demanding games at good framerates. Haswell Refresh has i7 chips that go down to 35W which is crazy - you're looking at a system that can capably play Crysis 3 at 30fps at 1080p and only draw 100W at full load (assuming it's not a CPU limited game).