IMHO, Science Fiction and Fantasy are mainstream now. We live in a SF/F world with our cell phones, aka mini super-computers in the palms of our hands, quantum dot televisions, privatized space travel and all the rest. Almost all the highest worldwide movie grosses have been in the SF/F ouvre, e.g. Avatar, Marvel's The Avengers, Harry Potter and the Deathly Hallows Part 2, Transformers: Dark of the Moon, etc. Conferences like Comic Con and their imitators are rampant. Many of the most popular TV shows are in the SF/F genre, such as Big Bang Theory, Supernatural, The Vampire Diaries, Once Upon a Time, Person of Interest, Revolution, Beauty and the Beast, Arrow, depending on which list you consult.
Even if we just focus on fiction, what do we see?
What were the best-selling books in 2012? Yep, you guessed it, many science fiction and fantasy titles, including The Hunger Games, Catching Fire, Mockingjay, Heroes of Olympus: The Mark of Athena, The Hobbit, A Game of Thrones, The kane Chronicales: The Serpent's Shadow, A Dance With Dragons, Abraham Lincoln: Vampire Hunter, A Clash of Kings, A Storm of Swords and a lot more. And that doesn't even include the whole Twilight vampire series which was super hot in 2010 and before, and the whole Harry Potter series which was white-hot in 2007 and before.
Here's another indication SF/F has become prevalent: Doris Lessing won the Novel Prize in Literature in 2007, partly for her "space fiction"--as she put it.
So that's my 2 cents, SF/F is as popular as Gangnam Style. :)
What do you think? Ghetto, or Gangnam Style?