As I pointed out in my AJAX post, I think difficulties of writing AJAX make it a poor web application platform, particularly since there are easier alternatives.

Flash, for example, is a better platform for some applications than AJAX because it offers similar capabilities (i.e. XMLHttpRequest in DHTML) and comparable, if not better, level of availability along with much better graphics capability.  Flash tool developers such as Lazlo and Xamlon makes it easy to develop interactive web application.  Just take a look at this Google Maps like demo built over a weekend using Xamlon's upcoming tool.

Note that AJAX in Flash is inappropriate for web applications that manipulate DHTML DOM extensively and has a number of issues that makes it prohibitively expensive for uses beyond demos and small tightly-focused applications.  For example, you can't built PhotoShop with it without abandoning usability.

Beyond Flash, .NET looms with superior functionalities and flexibilities.  The only thing it lacks is the availability in several sense.