I have created a PHP class library to facilitate the easy development of web based applications that use Ajax to communicate with the server asynchronously and update web page content. I call my library xajax.
There are usability issues to be considered, but the potential is exciting.
My xajax library homepage is at http://xajax.sourceforge.net.
I would love to see the Bloggernacle become a leader in blogging innovation. Feel free to explore possibilities here in the comments.