Today's GalleyCat has an interesting post about genre. Ron Hogan asks the question, "Can a book be both urban fantasy and paranormal romance?" Hogan references the Harry Dresden modern wizard books by Jim Butcher, Laurel K. Hamilton's vampire novels, and Charlene Harris' Sookie Stackhouse books (more vampires). Hogan rates Harris and Hamilton's Anita Blake stories as having "explicit romance components," but considers Butcher's as "more of a mashup of hardboiled mystery and magic—Mickey Spillane meets Solomon Kane." Part of Hogan's point is that readers (mostly female readers) who don't think of themselves as "fantasy fans" are more likely to still read and love both Sookie Stackhouse and Anita Blake, vampire killer, than non-fantasy readers are to fall for Harry Dresden.
The post has some interesting points about genre, but the point I want to make is that genre in print books can be a limiting factor. Bookstore clerks need to know where to put a book. But in a virtual world, books can be tagged with as many labels as apply, which could lead to mystery readers tripping over Harry Dresden. The "get a free sample" feature that works so well with ebooks could make them take a chance on something new and like what they read.