My experience won't add much to what people have already said, but I'll write it anyway:
Before discovering MobileRead (and the dedicated e-reader devices), I used to read on my old laptop (with LCD screen). I've spent years doing that, because I already had MANY ebooks, especially free RPG handbooks from independent gamedevelopers (I was, and still am, an avid roleplayer :P ), and sure my eyes felt like burning at the end of the day.
I switched to an e-ink reader, and suddenly reading became "easier on the eyes" as many here say.
BUT (and I write it in bold before someone skips the rest of the comment labeling me as an e-ink fanatic): rather recently, for several reasons, I had to read again on my laptop, spending hours on it. After reading several LCD-vs-eInk topics here on MR, I tried several suggestions I got, I spoke to my eye doctor, and the result is that now I can read on my LCD laptop screen with no problem. All I had to do was... turn on the lights. I mean, the room's lights.
Yeah, did I mention that I mostly read in my bedroom with dim lights?
In that situation, the backlight of my screen "stands out" against the darkness of the surroundings, so my eyes have a hard time keeping focused on the page: if the "center" of your eye's field of vision is brightly lit, your eye's pupil tends to shrink, but if the "margins" of your eye's field of vision is dark, your eye's pupil tends to enlarge to capture more light (so you can see what is there "around"). This continuously makes your eye's pupil move (shrink, enlarge, shrink, enlarge...) and its muscles grow tired.
Instead, if the room's light is at the same level as your screen's light, your eye doesn't need to adjust so often.
At least that's how I understood what my eye doctor told me, I might have gotten it completely wrong and I am by no means a specialist in this field, so please don't beat me (too hard) if I got it all wrong
So, by either dimming my monitor's brightness or by turning on the room's light, and by reading sitting on a CHAIR at my DESK instead of reading sitting on my bed, the LCD screen doesn't bother my eyes anymore.
I do use my e-reader, though, much more than my laptop, for the simple facts that it's less heavy, less encumbrant, has a longer battery, and takes less time to get from pressing the "ON" button to actually reading
