Some more links on XMLHttpRequest, which I wrote about here:

• At Adaptive Path, Jesse James Garrett writes Ajax: A New Approach to Web Applications. JJG defines Ajax as:
  • standards-based presentation using XHTML and CSS;
  • dynamic display and interaction using the Document Object Model;
  • data interchange and manipulation using XML and XSLT;
  • asynchronous data retrieval using XMLHttpRequest;
  • and JavaScript binding everything together.

  The article continues to break down the differences between traditional web applications and Ajax applications.

• XMLHttpRequest, Ajax, and the customer experience cautions that Ajax is a new technology and that its benefits come from the application of the technology to existing or new user interfaces. If someone's used to one way of doing things on the web (check off form items for example and then search for the Submit button) and we change the underpinnings to use XMLHttpRequest, we need to consider the impact on the user experience.
• Very Dynamic Web Interfaces is a walkthrough and demo of using XMLHttpRequest and Javascript.
• Guide to Using XMLHttpRequest (with Baby Steps) is a nice tutorial on implementing XMLHttpRequest
• XMLHttpRequest Introduction is an introduction to XMLHttpRequest and a number of tutorials, examples, and tools to implement it.
• Movable Type な Blog の全エントリを JavaScript with XMLHttpRequest でインクリメンタル検. My Japanese is poor but I think this is an entry about using Ajax/XMLHttpRequest to perform incremental searches of MovableType entries.

My own work with XMLHttpRequest was on hold for awhile but I've started playing with it again and once I finish my !*@&#^! web site redesign (much easier when you have a team of smart people to work with. Frisket is not so good with PHP or HTML).