Oh yeah, AJAX totally rocks. Hardest part about it is that whole cross-compatability stuff with other browsers and such. It's wonderful if you're using it for personal projects (which is what I do with it). It can make everything seem so seamless!
If anyone is wondering, straight out of wikipedia:
AJAX or Asynchronous JavaScript and XML is a term describing a web development technique for creating interactive web applications using a combination of:
HTML (or XHTML) and Cascading Style Sheets for presenting information
Document Object Model, JavaScript to dynamically display and interact with the information presented
XML, XSLT and the XMLHttpRequest object to interchange and manipulate data asynchronously with the web server (although AJAX applications can use other technologies, including preformatted HTML, plain text, JSON and JSON-RPC as alternatives to XML/XSLT).
Basically you use javascript as the link between the client and the server. You use XMLHttpRequest to grab XML from a server and parse it again with javascript. Excellent examples of AJAX in use are GMail and Google Maps. It's also been showing up recently for blogs, forums, and online chats, to make things seem more integrated by not constantly refreshing the browser.
Some good reading, if you're interested, is:
http://developer.apple.com/internet/...mlhttpreq.html