I often have problems with eye irritation/fatigue after a long day of work and thought an e-ink device would make night reading easier. Got a kindle touch, tried it for a week. It was worse, without a doubt. I tend to read in dim light (indirect lamp), and found that the kindle needed direct light for me to easily read without eyestrain. iPad with very low brightness, or even in reversed accessibility mode is nicer. For me, that is. And, any book or paper with code samples just doesn't work well on a small e-ink screen.
If it's articles with diagrams and colors or magazine layouts, with gloss and shine, nothing beats iPhone 4(s) and iPad 3's retina display.