I tried reading a book on my phone a while back. I read for about 40 minutes and then spent the next hour or so convinced that I was permanently cross-eyed.
Seriously though--maybe my eyes are weaker than most, but I just can handle the screen and have yet to meet someone who can read for an hour or two at a time without significant eyestrain.
Were you doing black text on white, or white text on black? Switching to the latter was what made the difference for me. I've read for many continuous hours on my phone.
That's my issue with phone reading. I can't just pick up any arbitrary pdf and read it comfortably, it has to be specially-formatted, or else you have to side-scroll and all that annoying stuff. And the pdf's I want to read are rarely formatted right.
You'll find that to be a big problem with any ebook reader except perhaps the kindle DX. I feel your pain though. I looked for months for an ideal ebook reader for academic papers, and concluded that such a product didn't yet exist.
Seriously though--maybe my eyes are weaker than most, but I just can handle the screen and have yet to meet someone who can read for an hour or two at a time without significant eyestrain.