Useful for the programming forums as it would help people to reinforce correct answers. However, rather than just a "like", I'd like to see a "like/dislike" or a "thumbs up/down" system that allows us to thumb down bad answers to programming questions.
I can, however, see any system of this type including what is currently in place causing issues in the heated debates that tend to go on in General Discussion. Perhaps you can find a way to limit the Like/Dislike to the programming forums only.