I'd like to weigh in on the side of not having "like" and "dislike" buttons. If this site is here for teaching and sharing purposes, it would add an unnecessary discordant note to be able to negatively judge posts with the push of a button, rather than quietly informing Dave if a post steps over a line.
Edit: I just realized, if the buttons are meant to judge threads as a whole rather than posts or individuals, I still feel the same. Everyone has a different opinion as to what is interesting or important, and I don't see any need to sit in judgment with the push of a button rather than just not posting on the thread or talking to the person.