If you like playing Texas Hold-em and are interested in the fuss about the use of AJAX, try gpokr.
AJAX-based web interfaces achieve quick responses to user input without loading new pages. When you click a button, for example, the existing page instantly updates with new information. They also tend to use innovative widgets that are not part of the standard HTML paradigm.
AJAX is important because it eliminates many of the limitations of web interfaces, which include clunky widgets and slow response times. The drawback is that users may not be familiar with the new ways of accomplishing their goals.