Ray Kurzweil: The singularity is near
The primary failure is the inability of many observers to think in exponential terms.
I think one important caveat to the unbounded thinking of the exponential growth of technology is the energy limits that will quickly be reached if energy consumption continues on its current trajectory as well. I dug up this old link on Galactic Scale Energy that sums it up nicely.
Let me restate that important point. No matter what the technology, a sustained 2.3% energy growth rate would require us to produce as much energy as the entire sun within 1400 years. A word of warning: that power plant is going to run a little warm. Thermodynamics require that if we generated sun-comparable power on Earth, the surface of the Earth—being smaller than that of the sun—would have to be hotter than the surface of the sun!