In many cases AJAX can be used to simplify web form design.
Good example would be at www.launchsplash.com. Landing page is a simple form and the first form field implores you to enter a domain name. As you start typing you see the final result of what you are doing changing as you type right below where you are typing. When you type a dot your mode switches from sub-domain name to domain name form.
This kind of thing isn't going to work everywhere but it's an example of the power of AJAX and how it can be used to make form fields much simpler for the user. AJAX definitely doesn't make form fields simpler for the developer.
