I can't imagine doing lots of reading on a non-eink screen.
I know some people having trouble reading too long on it though. And they went back to eink.
This is mainly because I read in bed at night, and having a light on for the kindle would bothers my wife trying to get to sleep.
I rarely read with the ipad just because of size and weight. And to a lesser extent the non-retina screen.
Some people are really bothered by reading a backlit screen, but it doesn't bother me. I use the black background with white text and turn down the brightness and it works pretty good.