I went from one Sony PRS-500 to TWO Sony PRS-500s (the second one was on sale for $99 just prior to the release of the 505.)
I absolutely loved the 500, but then when I bought the 505 my love affair blossomed into romance and flowers and sweet words every morning.
I sold both 500s and bought the 505 around March (?).
For me, the 505 added an incredible leap in pleasure: It was faster, brighter, with a larger internal memory; there is no more image ghosting; it's lighter and has a better ebook cover (the cover doesn't sag like the 500 does).
Next to a computer and my Thorens turntable, I've never had as much pleasure as owning an ebook Reader. My "ebook-loving" days goes back about 7 years ago.
In my opinion, ebooks have finally caught on, and people and publishers (generally) are now starting to "get it" [understand].
I have to confess, though, that even though I own another ebook reader, I use my PRS-505 every single day - not one day has gone by that I haven't been reading in it and marveling at the technology and loving it.
When reading on an electronic device, I am a serially monogamous reader with my Sony PRS-505. When I get married in December [tentative date], my wife will have to understand that my ebook Reader will also be with me on the Honeymoon.