Yes, AJAX is very cool. This is a newer combination of technologies that allows instant, more interactive web content through communication between client and server without refreshing a page (GoogleMaps is most common example). But this can only work if the user agent (a.k.a. browser) has Javascript enabled and can handle XMLHttpRequest. There are also usability issues, such as the user not being aware of automatic content and formatting changes. What are your thoughts? Experiences?
Check out this great article on the subject from WebAim on the subject:
Accessibility of AJAX Application