The black lines/broken-looking-but-not-actually-broken-screen problem isn't uncommon, but it's not something restricted to Kobo devices; it's more of an issue with the EPD screens. I can't speak for the Nook, but where I work, we sell Kindles, and it tends to be one Kindle every two weeks with a stuffed screen. We did also have the same issue with the previous e-readers we sold, which were also E Ink, but previous gen screens (8 level greyscale).