Researchers from Sophos have spotted a currently circulating "Enable Dislike Button" Facebook scam.
Upon clicking on the what looks like a recently added genuine Facebook feature, users are exposed to a "Follow the steps below to get the Dislike button" instructions page similar to the one seen in the Osama Execution video scam.
Facebook now has a dislike button! Click 'Enable Dislike Button' to turn on the new feature!
For the time being, Facebook doesn't offer a dislike button.