> Having said that... must be at least a year since YouTube switched from 5-star ratings to positive/negative ratings. Maybe it's not totally relevant here, but I'm interested in what effect the switch has on ratings.

I think conceptually they are different. +/-, yes/no, thumbs up/down work best "would you recommend this?", just like "liking" or "+1"ing, or up-voting links on HN and reddit.

Star-ratings are still best for when you critique a more extensive piece of work, and may be accompanied with a review. "This book is good and I recommend it, but I think xyz is better and it lacks from these reasons, so it gets 3.5 stars."

Both are relevant and different ways of designing user-feedback, and certainly too often companies have mistakenly used 5-star rating when a binary recommendation is more appropriate.

Probably the best example is bulletin board/forum systems. They all seem to come with 5-star ratings for threads, but conceptually it makes no sense. You don't critique a conversation as "well this conversation is interesting, but not as good as this conversation, so i rate it 4 stars out of 5. OP: Next time i would recommend writing things more in this style for a certain 5-star thread next time!"

Here conceptually, you either recommend a thread ("check it out!") or vote it down ("this isn't worth your time clicking on"), a la links at reddit and answers on SO.

Most youtube videos are the same, as the vast majority are single-concept videos, be it music videos, comedy, sketches or otherwise, often just 2-3 minutes in length. Either you recommend it or you don't.

But multi-star ratings still makes sense in contexts where your review is multi-faceted. A hotel may be good for some reasons, bad for others. Longer experiences (say a vacation, extended experience with a business), and long-form media books, feature-length documentaries etc, are still appropriate for a star system.