I stumbled across an update for this "API" in my travels. It is a very interesting approach to web application development. Its not so much a technology as it is an approach. Jesse Garret sums it up very nicely:

"Take a look at Google Suggest. Watch the way the suggested terms update as you type, almost instantly. Now look at Google Maps. Zoom in. Use your cursor to grab the map and scroll around a bit. Again, everything happens almost instantly, with no waiting for pages to reload.

Google Suggest and Google Maps are two examples of a new approach to web applications that we at Adaptive Path have been calling Ajax. The name is shorthand for Asynchronous JavaScript + XML, and it represents a fundamental shift in what’s possible on the Web."

There is a .Net (of course) implementation here: http://ajax.schwarz-interactive.de/ with examples:

C# -- http://ajax.schwarz-interactive.de/csharpsample/default.aspx
VB.Net -- http://ajax.schwarz-interactive.de/vbnetsample/default.aspx

Updated link (simple implementation):
http://www.15seconds.com/issue/050526.htm