Q: How many GRRM fans does it take to change a light bulb?
A: None, the new bulb hasn’t arrived yet.
Q: How many Harry Potter fans does it take to change a light bulb?
A: A few thousand, at midnight, in Barnes & Noble.
Q: How many Discworld fans does it take to change a light bulb?
A: Three. One to change the bulb, and two to ask, “What color?”*
*Okay, so that’s a little lame. You think up a better one.
Q: How many Stephen King fans does it take to change a light bulb?
A: Don’t bother. You’ll just have to change it when it burns out again.*
*Cheap shot at the Dark Tower books.
Q: How many emos does it take to change a light bulb?
A: None. They’d rather sit in the dark and whine about it.
(Updated from the 80s, when it was a joke about The Cure.)
Yes, but emos aren’t fantasy fans.
Can easily alter to: “How many Vampire: the Masquerade players…” then. 
Okay.
Q: How many Heinlein fans does it take to change a light bulb?
A: Only one. Because if you’re not self-sufficient enough to change it yourself, you don’t deserve to have the damn light bulb changed.
Q: How many Twilight fans does it take to change a light bulb?
A: None. Their light bulbs last forever. And sparkle.
Q: How many Doug…
A: 42!
Personally, I would go with
A: The number between seven and nine.
win