Man, I have lived in Europe for the past 11 years and have yet to meet anyone who has used them or commented on them. I know someone who went on vacation to the US and took an overnight Amtrak for fun.
I’m sure they exist but really, people fly on longer voyages. Bullet trains may be changing that. A Madrid->Paris line will open soon that’ll do it in 5 hours. Which gets close to the speed of a plane when airport security and the like is taken into account and should give much more comfort.