Lucy Kinder at the Telegraph says:
Facebook is developing a ‘sympathise’ button as an alternative to the ‘like’ button.
If a user tags their status with a negative emotion, then his or her friends will be able to ‘sympathise’ with the post rather than press the ‘like’ button.
Of course, Facebook will never have a “dislike” button because Facebook is an advertising platform, and everything on Facebook has to be happy and like-able all the time. That’s the problem with Facebook.

Dislike.
Facebook is no place to let off the steam from your pathetic nerd rage. Now if you excuse me, I have to like a video of a distant acquaintance’s child, not that I have any intention of watching it
Wow, what an advancement! Good thing they aren’t out of ideas.