Good comment at Brad DeLong's

"To some extent, the exponential increase in computer power is illusory.

Hardware gets faster & faster, but programs get bigger and attempt to do more. Disk drives get bigger, but so do the files to be held. Modern desktop machines draw more power than older ones in general, despite improved efficiency. So exponential growth is not sufficient to grow out of problems. Supply growth must exceed demand growth, or you get nowhere.

Additonally, exponential growth in complexity of semiconductors will not be able to harvest more energy from sunlight than is there. There are finite limits on how efficient transportation technologies can be. Assuming that exponential growth can continue indefinatly is most assuredly wrong."