Originally Posted by jackie_w
I don't know whether davidfor is planning to do more work on the Calibre device interface plugin so that SD book thumbnails work just like internal memory ones. Based on past experience if it's technically possible he'll do as much as he can for everyone.
From earlier posts, he is working on that. With 2.5.0 firmware, some of the sleep images looked very odd. On my Glo, I replaced a couple of them with the correctly sized images and they looked fine again but not planning on doing that for 1500+ books manually. At least, the images will now be cached on the SD card so they will only need to be generated once.