i have both. bought the sony reader 505 in the us while i was travelling there and decided that carrying all the physcical books with me was too much. and sending them back home was getting too expensive since the us postal stopped the special book rate to send stuff back home.
i agree with joec concerning the looks of both. i decided to buy the cybook because the ability to buy new novels in the mobipocket format without the hassle of formatting and other technical things that i need to know about.
i'm addicted to reading books and less a computerperson.
and then i discovered that leaping gnome on this forum is willing to buy credits for non us residents so they can buy 'new' novels from the sony store. altho' that's an opportunity to get new books i'd rather have the feeling of being independent.
differences in some features: control, filtering, greyscale, booting is quicker with the sony, when you stop reading and start again the sony opens up the page that you just left, like the fontschoices in the cybook, the lightness of it. mobipocket format is a big
matter of taste i guess and if you want newly published books.