I would love to have a guy or two in my book group! I think it would definitely liven up the discussion and we would have a broader base of knowledge.
It may be difficult to find books that both genders would enjoy reading. I like nonfiction and action/thriller which seems to be the genres my husband enjoys most but I know a lot of women (many of them in my book group) who are not interested in those genres.
Your question reminds me of that book by Lorna Landvik, Angry Housewives Eating BonBons. They let a guy join the book club near the end of the book.
