Can't see much revolution there.<p>So they now have a plugin-repository and allow you to directly reference those scripts from your pages. That's great and all, except I don't <i>want</i> to embed external code that may change silently (or not so silently..) at any time.<p>Here's a tip: People flock to jQuery not because of some bells & whistles like a plugin-repo, but rather because it makes one hell of a lot of sense at the very core. It just feels right™ and allows for very short and elegant code. YUI? Not so much.<p>YUI feels more like someone took the "Java" in <i>Java</i>script way too seriously.
Not to mention YUI 3.1 is released this week, 3/30/2010. On top of some new functionality, the development team is porting a lot of YUI2 widgets, fixing memory bugs, and cleaning up some of the abstraction.
I am patiently waiting for YUI3 to finally reach the feature level of YUI2. I've used version 2 on a few projects and it was a pleasant experience all-in-all.<p>The only downsides were it was too heavy and too verbose.<p>I often resort to JQuery when i need DOM manipulation because its nowhere near as verbose as YUI2.<p>As for the too-heavy thing, it was a compromise because it provides one of the richest widgets in all JS libs out there.(plus YUI3's module system is supposed to help)
Lots of people that have been using YUI2 will appreciate the new YUI3 modular concept. While using YUI2 if you wanted to use a basic version of a YUI widget/component you would have to include the all of that widget library. Now that has that behavior has changed and most of the widgets/components/modules have been divided in several smaller chunks that make sense. For example, YUI3 IO has io-base, io-xhr, io-form, io-queue etc. You could load any one of them depending you needs. No need to load all of IO.<p>YUI3 has chaining similar the jquery (not as clean, I think) which makes is less verbose and pleasant to write JS.
YUI3 is much better than YUI2, and they learned a lot from jquery in making it expressive / terse. I even spent the better part of a week learning about YUI3 thinking I might use it instead of jquery. But then I found, and it's hard to explain exactly why, that I was much less productive with YUI3. I think that jquery is just so damn intuitive to use, I usually can guess how something will work. With YUI3 I was often left looking up something in the docs, or looking for an example (which wasn't so bad given YUI's excellent docs, but still, it's a hit when you can't just guess how something is going to work)