I did a bit of quick "research" (i.e. Googled a bit), and the most interesting page I found was an article on the NYT:
http://bits.blogs.nytimes.com/2010/02/12/do-e-readers-cause-eye-strain/?partner=rss&emc=rss
Good quote:
> “The current problem with reading on screens is that we need to adjust our bodies to our computer screens, rather than the screens adjusting to us”
So it's possible that the ergonomics of reading on a laptop/desktop have more to do with strain than the type of screen technology.