Some people may long for the simplification of genres, as writers and teachers like Aristotle classified them in earlier times. He described two basic types of plays: comedy or tragedy. Others thrill to the various ways in which people can be inventive through book genres. The proliferation of different book categories means there is always something to read that is likely to appeal to someone.
For those who have ever wondered how many different books are out there in the world, Google has an answer for you: 129,864,880, according to Leonid Taycher, a Google software engineer who works on the Google Books project.