I had a post related to this over at TeleRead. The bottom line for me is that I don't have a single 'perfect' device. In different situations I want different form factors. If I start reading on my desktop, I should be able to sync my progress to my smartphone or e-reader and take it mobile.
The article is here:
http://www.teleread.org/blog/2007/12...n-book-reader/
Michael