Jesse James Garrett, who wrote The Elements of User Experience blogged on Adaptive Path about ajax: a new approach to web applications. He explains,

An Ajax application eliminates the start-stop-start-stop nature of interaction on the Web by introducing an intermediary — an Ajax engine — between the user and the server. It seems like adding a layer to the application would make it less responsive, but the opposite is true.

He says, “Google is making a huge investment in developing the Ajax approach.” Garrett follows this with a list of Google projects, such as Google Maps, that are Ajax applications.

Ajax is ‘Asynchronous JavaScript plus XML.’. I keep thinking of JavaScript as old technology, but this will make me reconsider taking a class in it. According to Jeffrey Veen’s blog entry, Scrubbing Innovation into Interaction: Ajax, Ajax “exploits the clumsily-named XmlHttpRequest Object,” which has been around for awhile. There is a long discussion about Ajax on QuirksBlog: Ajax, promise or hype?

Article:
Will AJAX help Google clean up? | CNET News.com

W3 Schools tutorial: XML DOM - HttpRequest object