I was one of the ones who jumped on the AJAX bandwagon pretty quickly. I've built several private apps using AJAX, and really like it. I like the fact that the web becomes more "rich," and more closely resembles forms in functionality. The gains are enormous.
That having been said, I found myself asking the question: Is it worth it? I've found (so far) that doing things with AJAX takes at least three times longer, there's much more room for error, and cross-browser issues are brought to the forefront. I have played around with the AJAX.NET framework a little, and have had mixed results. What I got working was pretty cool, but do I really need rounded corners on divs? It seems to me that a lot of their controls are gimmick-ey, and don't really have all that much to do with AJAX.
I think my biggest disappointment with the MS AJAX.NET framework is it's complete failure when adding the framework to an existing project. I could not for the life of me get it to work. I spent three days fiddling with it, and nothing seemed to want to work. I really have little desire to re-write the projects that I do have for the benefit of AJAX.
So, is it all worth it? Are post-backs really that evil? I'm starting to think "No." AJAX is cool. I probably won't use it if I'm in a hurry. It has its place, but is it ready to take over the web? Should it?
Those are my questions...