I have the Mini and love it, but I have not really test driven it for marathon reading. I've had it almost a month and it is a great little tablet, the lighter profile being a major asset IMHO in terms of travel and for using it in bed before going to sleep. It is much lighter and easier to hold. The screen is fine for my uses.
I am one of the lucky ones who received a good PW from the get-go. I enjoy it tremendously and use it mainly in the evenings. My K3 workhorse is still going strong and it goes to work with me in hopes I can sneak in a little reading during lunch.