Farhad Manjoo claims to have revealed it:
How does this one site come up with so many simple ideas that people want to spread far and wide? What’s their secret? The answer, in short, is that BuzzFeed’s staff finds stuff elsewhere on the Web, most often at Reddit. They polish and repackage what they find. And often—and, from what I can tell, deliberately—their posts are hard to trace back to the original source material.
Ezra Klein defends Buzzfeed.
The Dish 