In the last year, I've seen a number of new web applications with nice rich UI interface, and most of them are standards based, so multibrowser-mulitplatform (thanks to firefox). I'm talking about things like the SelectContactControl of GMail.

Today I've learned this new way to build responsivness user interfaces with we technlogies is called AJAX

http://www.adaptivepath.com/publications/essays/archives/000385.php