What do you think of the current implementations of AJAX (Google Maps, Writely, Google Suggest, Zimbra, etc.) on the Web today?
They are irrelevant for the vast majority of business web sites. (And by "business web site" I also mean sites for government agencies and non-profits.)
A business site will profit much more from writing better headlines than from sticking a programming trick on its pages.
.... The very nerdiness of the name "AJAX" gives me hope that it will be used for causes more worthwhile than those now characteristic of Flash. Doomed by its own name, Flash had similar potential but was so grossly abused for "flashy" design that it never succeeded in adding much useful functionality to the Web.
Since AJAX is an engineering idea, it has the opposite problem of leading to featuritis. Remember: just because you love technology and advanced features, it doesn't mean that your customers do.
-- Interview with Jakob Nielsen