Forget the introvert/extrovert trap that so many comments/articles fall into.

I don't join book clubs precisely because I don't want to commit to reading that material on that schedule. The idea of simply meeting up with friends for an hour to silently read whatever we feel, hey, I like that. I can read LotR or HP again, someone else can read sci-fi or mysteries, and we can chat about that or whatever else. It's a great alternative to reading one and only one book.