Kurzweil also ignores economics. The advance of technology is driven in part by economic forces. Computing power may stagnate not because we have reached physical limits but because present-day computers are good enough for what 98% of the market wants.
I see this trend developing. If anything, the trend in consumer computing is toward less powerful but lower-power and more portable computing devices. My current laptop -- a Macbook Air -- is actually slower than my previous laptop. But it is more portable and uses less energy. And it does everything I want. I don't need more power right now.
The only areas driving the performance end are gaming, high performance computing, and high-capacity data centers. How long will those go until they too are basically satiated?
We've seen this in other areas. The envelope for aviation maxed out in the 1970s with things like the U2. Space flight seems to just now be emerging from a long coma with things like SpaceX, but on closer examination SpaceX is just reviving 1960s ideas and doing them at a lower cost with modern control systems and materials technology.
My other reply about energy deals with supply-side limits to growth. This response deals with demand limits to growth.