A while ago I wrote briefly on why the Singularity might not be near and my estimates badly off. I saw it linked the other day, and realized that pessimism seemed to be trendy lately, which meant I ought to work on why one might be optimistic instead: http://www.gwern.net/Mistakes#counter-point
(Summary: long-sought AI goals have been recently achieved, global economic growth & political stability continues, and some resource crunches have turned into surpluses - all contrary to long-standing pessimistic forecasts.)
The continuation of the solar cell and battery cost curves are pretty darn impressive. Costs halving about once a decade, for several decades, is pretty darn impressive. One more decade until solar is cheaper than coal is today, and then it gets cheaper (vast areas of equatorial desert could produce thousands of times current electricity production and export in the form of computation, the products of electricity-intensive manufacturing, high-voltage lines, electrolysis to make hydrogen and hydrocarbons, etc). These trends may end before that, but the outside view looks good.
There have also been continued incremental improvements in robotics and machine learning that are worth mentioning, and look like they can continue for a while longer. Vision, voice recognition, language translation, and the like have been doing well.
A very large chunk of this is directly or indirectly increased resource prices, especially driven by China.
If the improvement in cost-performance of computation slows dramatically in the next decade or so, this could be a small effect. Kurzweil predicts that silicon CMOS will end and be replaced by something that improves at least as rapidly, generalizing from past transitions (vacuum tubes to transistors, etc), but there are fewer data points to support that claim, and we are much closer to physical limits, with less room for miniaturization. There are new materials with plausibly better properties than silicon, room for new designs (memristors, unreliable computing, wacky new cooling systems), clever 3-D innovations, and so forth. However, a grab bag of such innovations seems less reliable than miniaturization, which automatically improves many dimensions of performance at once.
Impossible to estimate.