Via Sonia Arrison at Volokh Conspiracy:

New technologies are almost always adopted by the rich first, but over time they eventually reach everyone, and the historical record shows that the distribution of new technology is speeding up, not slowing down. 
For instance, it took forty-six years for one-quarter of the population to get electricity and thirty-five years for the telephone to get that far. It took only sixteen years, however, for one-quarter of American households to get a personal computer, thirteen years for a cell phone, and seven years for Internet access. A more vital example may be AIDS drugs which started off costing about $30,000 per patient per year 15 years ago. Now, better drugs are available and cost $100 per patient.

I got into a brief related discussion with @RL_Miller this morning on the diffusion of clean tech in developing countries. Global energy use is expected to at least double by 2050, and 90% of that growth will come from developing economies. The generation sources for that energy will make a bigger impact on emissions and climate than any other factor.

If developing economies are able to "leap-frog" grid-scale coal-fired power and go straight to clean energy generation, then we may avert climate catastrophe. However, that requires cheap and scalable clean tech, which we just don't have yet.

Fortunately, as Ms. Arrison notes, global rates for technological adoption are accelerating. Energy is complicated, of course, because the end-user buys energy services, not energy-generating technologies. But it's still encouraging to know that when a new, useful technology comes around, we're getting better at picking it up.