"The other big issue to me is that the screen resolution on the kindle is lower. I really notice the difference between my 500 and 505."
Screen resolution is 167-170 PPI in all three devices. If you can discern a two percent difference in resolution, you have REALLY good eyes! ;-)
The difference between Sony's 500 and 505 is not resolution, but contrast. The 505 and Kindle both use exactly the same display, the latest E-Ink "Vizplex" panel, which has substantially better contrast than the older panels used in the 500. (I have both 500 and 505).
In short, the Kindle's resolution is NOT lower than either of the Sony Readers; and its contrast is exactly as good as the latest Sony Reader's.
Andy Baird
http://www.andybaird.com/travels/