I'm surprised calibre doesn't come with a standard tag for genre.
I like to keep the date each book was placed on the ereader, so I'll have a column per person for that.
Then I'll have a column per person with a numerical value (rather than stars, which is blank for 0)
0 = Ignore
1 - 5 = Rating (of author, not book)
That way using a search I can exclude the 0s for that person (and read, if wanted.)
This particular friend cannot remember the names of authors, so he has a little notebook where he can write a little note to remind him about the book for future searches of that author. So I'll have to have a column for his comments.
He's especially pleased to have an ereader because he has cataracts, and with a large font he can actually read books again.