One question that can always be added to any book discussion is, "If you knew nothing about this book, and you saw the cover on display in the library, would you pick it up?"
This one question can then lead to all sorts of additional questions such as:
Does the cover accurately depict the contents of the book?
Who does the cover appeal to? Is this the book's intended audience?
What does the placement and font size of the author's name tell you?
Do you think the jacket artist is male or female? Why?
What would you do differently?
I came across an extremely interesting discussion on trends in cover design on the First Things blog. It could be the basis for an interesting library program, or for a discussion in a book group.
The Book Cover Archive, "for the appreciation and categorization of excellence in book cover design," is a look at more than 1,000 book covers! The site also provides links to other places to go for information on book cover design.