I have implemented AJAX style comments system. If you click on the ‘Add Comment’ button below you can see it. The difference is that now you are presented with a comments form appears within the existing page instead of a comments form being on a new page, as was the previous behavior. This is AJAX, and it is the technology that people are calling Web 2.0.
What’s the big deal you ask? By having the ability to only update parts of a web page instead of updating the whole page every time you invoke some function, it makes the browser act more like a desktop application than a web page. The end result is more robust applications served over the web. Think google maps or facebook.