The Vitamin has a post on 15 things you can do with the Yahoo! UI. I have to admit, Yahoo did a pretty good job of creating the library. A lot of the features are pretty slick and can help us developers when we are creating Web 2.0 applications. I used to be opposed to using others components and felt more comfortable using my own widgets that I created. I have learned to use my own as well as some of the other elements that others have created and it has helped increase my efficiency tremendously.
The site has quite a few demos and tutorials using the Yahoo! UI. I think that many of us can incorporate these easily in every day use of Web 2.0. There’s quite a few different libraries that I use. Most of them do the same thing but I look at my projects on a larger scope. The one that has the most features for the project I am working on helps me decide which one to use. If course some are easier to use than others and some have better documentation. After using them a few times it always gets easier. I hope this tutorial helps.