If you're interested in my $0.02 on AJAX, check out my Public Static editorial in JavaPro magazine. Here's an excerpt:

If your head wasn't in the sand during 2005, you've probably heard of AJAX (Asynchronous JavaScript and XML). Just in case you're wiping the sand out of your hair right now, here's a brief overview. AJAX is a rebranding of technologies introduced in Microsoft Internet Explorer (IE) several years ago. These technologies, branded by Microsoft as Dynamic HTML (DHTML) include HTML, an implementation of Cascading Style Sheets (CSS), plus the ability to manipulate a page with JavaScript through the browser's Document Object Model (DOM).

Read, The Year of AJAX.