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.)
A lot of existing improvement trends would have to suddenly stop, along with the general empirical trend of continued software progress. On many applications we are well short of the performance of biological systems, and those biological systems show large internal variation (e.g. the human IQ distribution) without an abrupt "wall" visible, indicating that machines could go further (as they already have on many problems).
I'm not quite sure software is well short of the performance of biological systems in terms of what software can do with given number of operations per second. Consider the cat image recognition: Google's system has miniscule computing power comparing to human visual cortex, and performs accordingly (badly).
What I suspect though, is that the greatest advances in speeding up technological progress, would come from better algorithm that works on well defined problems like making better transistors - something where even the humans make breakthroughs not by v... (read more)