Mine's a year old Kindle keyboard wifi and I had some issues occasionally with it freezing when there were 600+ books on it. I factory reset it and only loaded 200 or so and haven't seen a freeze up since.
I haven't liked any of the new Kindle models, and your thread reminded me that mine isn't new any more, so an hour ago I asked my husband who happens to be at a US airport to buy me another KK.
