Everyone: Yeah, not particularly common, nor do they really add much.
PC gamers specifically (and series/ps5 now too, with those consoles supporting 120hz with compatible tvs and games): Quite popular, and they do significantly add to the gaming experience.
The banwidth for 4k at 60hz is only now becoming mainstream.
That means when I bought my current laptop, still under the 3-year warranty, I would have had to get something worse to get HDMI 2.0 support, since I compared everything available.
IME even non-techies find 30Hz uncomfortable to use.
Definitely not my thing too, I'm all in for 120Hz, but it does have some niche uses at 30Hz.
