Anyone played with the Yahoo UI yet?

I tested some examples on their site and it looks great.

What it does is make it a lot easier to create complex menu's, animations, drag&drop and other nice stuff using javascript.

Just take a look at their examples what the options are.

Here is the link :
http://developer.yahoo.com/yui/

I've been using it for about a year and a half now, it's very good.
*EDIT*
maybe even longer than that actually

I'm not liking it at all. out of the huge number of examples, only a small handful will actually work in a custom environment (and that's with a ton of tweaking).

If you want your website to act like an app, your still better off writing the javascript by hand as the yui is somewhat useless in some respects.

I just started using the Uploader control, and it is nice. The flash/Firefox bug is a pisser though, I am now doing a work around for it, which is a pain.