Just imagine the impact on your brand's Facebook centered marketing strategy if you have more "hates" than "likes" on your brand's timeline.
When the original Like button was announced, Mark Zuckerberg made a bold prediction
there would be over 1 billion Likes across the web in just the first 24
hours. Sources at Facebook say Mark is estimating 2 billion Hates on
the first day. Facebook studies have shown the sad fact that people hate
things on the Internet more than they like things. There’s also an
internal debate on whether the new button should be called “Hate” or
“Dislike.”
Since the tiny Like button makes up such a huge part of Facebook’s
revenue, the introduction of the Hate button could raise Facebook’s
valuation further ahead of the IPO.
If FB decides to add the button, then personally I think "dislike" has a better ring to it than "hate".
Read more about the possibilities of hate button here