I'd say the like/dislike system has its place. Taking out dislikes would mean there'd only be likes, so all you'd see is, guess what: someone liked the video. *shokku* Despite that, I can't see how a dislike presents much in the way of criticism, all you can get from it is that someone didn't like the video. *double shokku* That's all it says, and I doubt there is a need to say both of them are a given.
It has a place, it's just not very helpful as constructive criticism; I agree with the few who said the star rating system is better for that but then again, I remember seeing a lot of videos that were rated either 1 star or 5 stars, so it wasn't exactly flawless in practice. Still sounds like a better idea to me as far as gauging how everyone percieves it quality-wise, though. It just sounds much more useful for knowing how much viewers like a video, at least on paper.
Wow, and to think that's all I have after eyeing this thread for like a week.