I read that post while I was away from home and did not have the opportunity to comment then. Also, there is rather a lot I want to say about the subject, more than what would have been appropriate in a comment.
One point in Nan's post was (not her own point, but quoted from a book) that
"if we use an e-reader or a laptop before going to sleep, our brains are affected so that we are more likely to sleep badly. It is something to do with blue light."
Before you read on, let me emphasise that the following are first and foremost my own thoughts and my own opinion, based on my personal experience. I am not a neuro-biologist and have never been to university. But I have read a few books and many articles about neurobiology and how our brain works (as far as scientists understand it), and am paraphrasing that information.
My thoughts on the topic:
The same is true for any other screen with back lights, such as smartphones, tablets, and the new generation e-readers. Even though you can not consciously see the "flickering" that comes from those lights (and refreshing), your optical nerves register it and send it to your brain. This makes your mind tire a lot more quickly as if you were reading from an "immobile", static source such as a sheet of paper. Then, it is your eyes that do the moving, not the reading material itself.
Another point that makes it easier to store and remember information from a physical book is the multi-sensorial effect. You do not only read the words inside the book with your eyes. You also touch the book with your hands, you smell it, and even when you are not reading it, you see it on the table, with the cover picture and the title printed on it. That makes for additional input; your brain connects all sensorial input to what you have been reading, rooting it more firmly in your memory than if you only read the words on a screen, i.e. your brain would deal with just the one info, not backing it up with other input.
My kindle is still the first generation. It has no back light, but uses a technology called e-ink. A layer of molecules is behind the magic - imagine those molecules as tiny balls, with one half painted white and the other black (or dark grey). When you "open" a page on your kindle, the letters you see are the black halves of the tiny balls of e-"ink", and the spaces in between the letters are the white halves showing.
|simplified representation of e-ink; picture from wikipedia
That is an extremely energy-efficient way of transmitting information to a screen, which is why the battery on a first-generation kindle lasts for a very long time before you need to recharge it.
This e-ink technology also means the reading experience for your eyes is very close to the one you get from paper. With one big difference: You can also read in bright sunlight without being blinded by the whiteness of paper. (There is plenty more about e-ink here on wikipedia.)
For me, my kindle has become indispensable. I still very much love reading printed books; they will never be entirely replaced, but my kindle is the best addition I can imagine. Nearly every day, I am on trains to and from work, and take longer train trips most weekends. I much prefer the lightweight kindle to a heavy book for those trips; also, a book can bend and get smudged so easily when you are travelling, something that does not happen with the kindle. Plus I can read on my kindle while waiting on windswept cold platforms, wearing gloves; that is very difficult with a physical book.
When I am home, I usually touch my kindle only to recharge it, and read newspapers and printed books.