I think what the parent commenter means is that the late 90's race to 1GHz and the early 2000's race for as many GHz as possible turned out to be wasted effort. At the time, ever week it seemed like AMD or Intel would announce a new CPU that was a few MHz faster than the competition, and the assumption among the Slashdot crowd was basically that we'd have 20GHz CPU's by now.

Instead, there was a plateau in terms of CPU clock speed and even a regression once we hit about 3-4GHz for desktop CPUs where clock speeds started decreasing but other metrics like core count, efficiency, and other non-clock-based metrics of performance continued to improve.

Basically, once we got to about ~2005 and CPU's touched 4GHz, the speeds slowly crept back into the 2.xGHz range for home computers, and we never really saw much (that I've seen) go back far above 4GHz at least for x86/amd64 CPUs.

But yet the computers of today are much, much faster than the computers of 2005 (although it doesn't really "feel" like it, of course)