Got a Kindle for Christmas, and so far I really like it, I esp like being able to adjust the size of the text and that it is light and easy to hold. I hadn't really considered that by being a Kindle owner I would have a different selection of books available than a Nook or Sony e-book owner would. I have no idea how different, but I found this app that seems to breakdown the barriers so that you can convert a book for Nook to Kindle format and vice versa. Go through the demo to see what it can do. e-book conversion
Cindy has been a Barnes and Noble customer so long, it was obvious that we would go with a Nook for her. She is considering buying an iPad... Not to replace her Nook, but for other functions knowing that she can download a Nook application and switch books between the two devices.
I have a Nook...my wife got a Kindle for Christmas...should be counter-intuitive but our reading tastes differ so much there wouldn't be much sharing going on anyway. They are both really nice...The nook can read ePub format and I think the Kindle can as well. Lots of freebies.