Visiting the book fair (which is honestly more of a book bazaar), one of the exhibitors I really disliked was Powerbooks. Not really apprehension but more of an inconvenience. The books weren't arranged by genre but rather by author. Whether you're fantasy, romance, horror, or general fiction, you were all lumped into the set of shelves. Which is fine if you have a small collection of books but not quite appropriate when you have dozens of shelves arranged in that way and a finite amount of time to browse through the books. Thankfully, this arrangement only applies to the book fair and not to their other branches. But what I do find peculiar at various bookstores to a lesser extent is how some books in a particular genre (in my personal experience, fantasy/science fiction) aren't shelved by series but by author. Troy Denning authoring a Forgotten Realms novel might be in the opposite side as R.A. Salvatore or Ed Greenwood, even if they're part of the same series. The same goes for other books penned by different authors but sharing the same world such as Thieves World or Conan. Or it might be a special reprint edition such as the SF Masterwork series or the Fantasy Masterwork series. It's convenient to have them in one area, arranged by series, instead of simply by author name. Personally, I prefer a mixed compromise between the two, a shelf being arranged by series (i.e. one area has all the Dragonlance novels, another area all the Lankhmar books) and then the rest of the shelf arranged by author (but hopefully the books of the author are arranged according to book chronology instead of alphabetically--in mysteries for example, having the top row of the shelf being occupied by Agatha Christie's Ms. Marple series instead of mixing it up with Poirot and Parker Pyne).
I was reading the last print issue of Dragon magazine and they have a featured entitled Unsolved Mysteries of D&D. There, they explain the author names Richard Awlinson and T.H. Lain (the latter I knew from a D&D article on the Wizards of the Coast site) are pseudonyms for several writers--the former for the Shadowdale trilogy set in Forgotten Realms and the latter D&D's iconic series. They state that the reason for doing so is so that the books get lumped in the same area of the shelf (and in the case of Richard "All-in-One" Awlinson, revealed the original authors in subsequent reprints). Of course this isn't the only application of collective ghost writers using pseudonyms. I always wondered how prolific Franklin W. Dixon could be writing all those Hardy Boys books (and the same applies for Carolyn Keene and Nancy Drew). It was a mixed surprise later on when I found out they were in actuality written by several different writers. And in many ways, I think the reason for adopting those pseudonyms isn't just to shelve the books in the same area but to give readers the illusion that they were all written by this one great author.