The more Ajax code I develop, the more I'm realizing that just because a form or widget or whatever can be done with Ajax, doesn't mean that it should be.

An Ajax-ified form takes several times longer to develop than a regular form. It takes longer to test. The source code is considerably more complicated; now you've got three languages to deal with instead of just two. And you can bet that it'll be harder to maintain.

I think a web developer has to weigh whether the usability advantage that would be gained by using Ajax is worth the extra time and effort that will be required to develop and maintain it as an Ajax app. If the usability advantage is slight, then spending 4x the dev time adding Ajax bells and whistles really isn't a good use of your time.