From the NYTimes article:
The admonition offered by legions of mothers — “Don’t sit so close to the TV” — isn’t really an option when it comes to e-reading devices. You have to get close to the screen to use it.
The act of reading is going through a number of radical transitions, but perhaps none is more fundamental than the shift from reading on paper to reading on screens. As consumers decide whether to make this jump and which technology to use, one key question is how reading on a screen affects the eyes.
First of all: doctors say that reading on a screen won’t cause any harm.