If you haven't peeked at the Yahoo! User Interface Library section lately, now's a good time. Some highlights: liquid layout, enhanced navigation, integrated blog and support group feeds, and YUI Theater ... check it out!
In other interesting news, we've just spotted the YUI libraries on MarketWatch. Click into any story linked from the front page and view source to see what they're doing. MarketWatch seems to have taken the global namespacing lesson to heart, and is also using the Event, DOM, Container, and Menu libraries to excellent effect.
Kent Brewster, Yahoo! Developer Network