I had originally intended to make my contact form AJAX but I decided to evolve my project as far as I could before adding in the AJAX technology. When I had the contact form working as good as it could, when I had added what I figured would be enough options to please everybody's preferences, only then did I look at what it would take to add AJAX.
When I saw how well my contact form works without AJAX, when I considered how much additional work it would be to add AJAX, and when I considered that probably contact forms aren't used that often anyway, so any bandwidth savings would probably result in only slightly improved speeds and any bandwidth costs would be improved by the AJAX only by a negligible amount.
The only reason I could think of to add AJAX would be to make this the
Ultimate Contact Form rather than the
Advanced Contact Form. In fact I expect to get smart on AJAX pretty soon, and one of the first things I'll do is probably come back and add AJAX to this contact form. And I'll rename it the
Ultimate Contact Form for SMF 2.0.
So make that definite "maybe" that I'll be adding AJAX sometime soon!

Probably after I get some more AJAX smarts than I have at present.