Putting books in the right categories is not as easy as it used to be. “In our mashup-crazy, zombie-besotted culture, genre-bending is a trend that shows no signs of abating,” writes Keir Graff on Booklist OnLine’s Read Alert service. Rebecca Stead’s Newbery winning “When You Reach Me”: Time travel? Mystery? Historical fiction? “Twilight”: Fantasy? Romance? As Graff notes: “If you put the right book in the wrong place, the right readers won’t find it.” This is where online catalogs and reference librarians come in.