This is a weirdly polarizing topic. I don't think I've ever clicked on the dislike button, personally (but I do click on the like button, occasionally). It would seem like people use the dislike button to signal that "I don't agree with the premise of the video" as much as it's to signal that "this video is actually crap". Same as with Reddit downvotes - it shouldn't be used for downvoting legit content that you don'…
Biggest miss is tutorials etc. Dislike ratio really useful to judge which ones are not worth the time.
I think that basing recommendations on a single dimension is flawed in its own right.