[kaufman]

This looks fine to me, but rather then creating a new column and grouping, wouldn't it be easier to just add the tags "Read" and "Reading" if the user told you to from the book details screen. You could even allow users to createn a list of tags they wanted to add in CC settings and then just select the proper one from a drop down. The nice thing about doing it this way is that it would handle purple lady's way of marking, it wouldnt require you to add a new grouping which you might have to hide for people not using it, it would be easy to make updates in calibre as well and if wouldn't force users to create new columns.

Just a thought.