Since last year, myself and others on the portal engineering team have been exploring AJAX for use with portlets and the Sun Java Portal Server product.  My teammate, Jai, has done a screencast demoing our latest work.  He covers the changes we have made to the "Enterprise Sample" portal to use AJAX.  We are using the DOJO toolkit libraries to add functionality to the portal container to allow asynchronous reloads of the channels for things like minimize, maximize, inline edit, etc.  It makes the "portal experience" much more compelling and brings Sun Java Portal Server in line with many of the new web portals (Google, Live.com, Netvibes, etc.) in terms of the expected functionality (using AJAX).