When to Use Ajax and When Not To
Just because your boss or your marketing department or you think that Ajax is cool and you really want to build an Ajax application doesn't mean that you should. If you understand what Ajax is good for, you'll be better off when you do get the call and can create an application that uses Ajax well, and not just for the sake of using Ajax.
What is Ajax?
Definition of the term Ajax as it relates to Web design and development
Ajax Security Hole
If you use AJAX to write applications, you should be aware of a security hole that was found.
Ajax (programming) - Wikipedia, the free encyclopedia
The Wikipedia provides a very clear and comprehensive definition of AJAX. This is a good overview site, but you won't learn to write AJAX from this page.
What is the Impact of AJAX on Your Life?
Understanding Ajax - Web Reference
A comprehensive review of Ajax and how to use it, from Web Reference.