Last summer Tim Dettmers published "The Brain vs Deep Learning Part I: Computational Complexity" an in-depth analysis of the computational power of the human mind, and also of the future trends in high performance computing (HPC). He makes a strong argument that not only have we underestimated the computing power of a human brain, we have also overestimated the growth potential of HPC.
I found this to be one of the most serious and extensive blog posts I have ever seen. I also thought his topics were interesting and relevant for the Singularity.
In the end he presented no obvious reason that the Singularity is impossible, or so far in the future we don't need to discuss it. His analysis predicts the Singularity may be decades or even a century further in the future than Ray Kurzweil has predicted. So we may not live to see it, especially if all we have are CMOS transistors to get there.