I don’t have a Kindle, but I’ve had Sony PRS-505 for more than a year. It’s a nice toy. Two things I primarily dislike about it: limited book availability and small screen size.

Kindle’s book availability is similar to Sony, and it depends a lot on what you read. If you mostly read mainstream stuff, you’ll find latest John Grishams and Dan Browns available online same day they show up in bookstores (though there are exceptions: for example, Harry Potter books are to this day completely unavailable on either Kindle or Sony Reader). Secondly, (almost) all books printed in the United States before 1924 are public domain. There’s a good selection of cheap formatted public domain books in Sony Store, and you can always download free stuff from Gutenberg online library.

On the other hand, less mainstream authors, say, Tad Williams (or even Robert Jordan), are often still unavailable on either platform, and paper is the only option. Same with textbooks.

As for the screen size, 6″ screen diagonal is just too small, and books are often formatted to leave a lot of margin space. You’ll have to flip pages often. I’ve been eyeing Kindle DX, but it’s still too expensive. Maybe some nice new models will come to the market in 2010.

I don’t really care for touchscreen and wireless connectivity, USB is good enough for me. Besides, I heard some scare stories about people screwing with your wi-fi enabled Kindle remotely.