By popular demand, here is a short 3 minute video tutorial on how to create a flat world using MCEdit. I tried to make it as easy to follow as possible, but you might have to watch in 720p to see everything.
How to feel cool on Minecraft forums:
>New Feature is announced
>Begin claiming it ruins the game "MINECRAFT ISN'T A BED/DOG/HAVING FUN SIMULATOR, IT'S ABOUT STANDING IN YOUR HOUSE WITH NOTHING TO DO ALL DAY REMOVE EVERY FEATURE GUH"