I started wearing them when I was 7, so at this point in time they don't bother me at all. I'm pretty sure they bothered me quite a bit back when I started wearing them, but I would still say my tolerance is quite high.
My older bother started them at the same time as me, and he couldn't handle it, so he swapped back to glasses after a few years.
I've used Ortho-k for 16 years, and I've absolutely loved them. I still confuse the heck out of people when I show or tell them I wear rigid contact lenses while sleeping. I've used glasses and dailies, and I without a doubt prefer Ortho-k. I do find it really weird that insurance doesn't cover it though - probably explains why they haven't become too widespread.
My older bother started them at the same time as me, and he couldn't handle it, so he swapped back to glasses after a few years.