Personally, I have frequently wished that the downvote button on youtube _comments_ wasn’t fake. (Last I heard, it currently doesn’t even send a packet to any servers when you click it. It used to, until google+ iirc [edit: see correction/update provided by voussoir in the reply. Turns out it does now. Thanks for the update/correction.])

The inability to downvote substantially alters what is said/ranked highly, I think.