I have a Nook, and I love it. But I did my homework because I'm avid reader. 76 books last year), and I wondered about back-lit versus e-ink regarding eye problems. I found out that avid readers should use the e-ink version, as it is like a book; whereas back-lit books should only be used if you don't read as intensely as it would be just like using a computer screen which is hard on your eyes. Also, back-lit books can't seen outside. To use an E-ink reader at night, as in bed, you must use a book light.
P.S. Kindles, Nooks, etc. are great for travel! I no linger carry seven books with me.