Asynchronous JavaScript and XML
http://www.adaptivepath.com/publications/essays/archives/000385.php
You will be seeing this idea more and more. It cracks open the last barrier between browser applications and other PC apps, and with Google showing off how cool it is, it is bound to stay. I've been watching it for about 3 years, and now it's getting the attention it deserves.
Woah, this is sweet. While looking into it, I discovered ASP.NET 2.0 has this built in, so I tried it out on one of my testing server. I put two huge data grids on the page, and gave one paging. The paging worked just like a charm, the call backs were transparent, similar to what gmail does. I'm hooked :)
Josh