As a 700 user, I am disappointed with Sony's new readers. The primary reason that I purchased the 700 was the built in light. I do a lot of boating and camping and the light is a big plus. Additionally, I can read in a dimly lit room while my wife is watching TV.
I was planning on purchasing one for her for Christmas. Guess I waited too long. I did not like the bulkiness of the add on lights for the 505. Will have to wait and see what they come up with for the 600.