Neat. If you can stand
However when you look around at what has already been done by other OSS libraries, YUI doesn't really add anything that is extra-ordinary special. Yes -- it has good clear defined cross browser support. Yes -- it has useful documentation. But is there anything new? YUI is on the "fat" side of the library in comparison to libraries like Scriput.aculo.us, but it is not "fat enough" to provide all the web gizmo a web developer wants (I want a tree/list control that emulates XUL's Tree control, thanks!). Hopefully more UI components are in the making.
Also with some of the examples I have looked at, I found it still lacks user accessibility from developers' point of view, i.e. it is not that developer friendly. For example, the Connection Manager library that does cross-browser XMLHttpRequest. Instead of performing operations on the object returned by
asyncRequest(), you need to keep on typing in
YAHOO.util.Connection... to check status, abort requests, etc. The same can be said about other libraries -- there are just way too much typing.
Honestly, I believe many other open source projects (or even commercial proprietary projects) will benefit from Yahoo! UI because it is indeed a high quality (though a bit awkward) piece of library.