What do I like & dislike about YouTube? I don't really go to YouTube, because I don't have the free time to spend looking at videos. Some are enjoyable and do brighten up the day. Our home connection can be slow, so it takes some time to watch some of the videos. YouTube also has videos that should even be on the site. Some videos are stupid. I wonder what the person's life is like and couldn't they be doing something more worthwhile with their time.
Libraries can benefit by YouTube in many ways. Your examples cover most of them - tours, events, services etc. But we do have to remember that there is still a group of people who don't use the Internet or computers. Maybe a kiosk at the library with some short videos running for those individuals.