I started reading at 10:30pm after being on the computer all day (eyes already slightly crossed). That said, I read for 1.5 hours and didn't feel any eyestrain. I did notice that under quite dim (bedroom) lighting, the 600 benefits from a book light more than the 505-- heightens the contrast. Of course, if my grandma were still alive, she'd be yelling at me for reading a pbook in that kind of poor lighting

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The background gray level is similar to the Kindle 2, though the K2 has a bit more contrast. The touch screen layer is well done, but it's still there-- it can never look *exactly* the same as an eInk reader that lacks touch.