@library addict: given that you had questions and that now you have gone through this, could you take a look at the
CC FAQ about Read info and tell me how it *didn't* answer you questions? Scroll down until you see "Marking books read and syncing that information with calibre". Now is the time for us to get this right, saving people confusion and frustration.
@LadyKoori:
@eschwartz: my preference is Yes for read and empty for not-read because it is visually cleaner both in CC and calibre. I don't (yet) have a real use for No, but might use it as a priority not-read (next to be read).