Last spring I wrote a 7,5 ECTS project at ITU along with a friend, Peter Madsen, on AJAX and it's usefullness for improving functionality in a web application - in this case website search.
It was kinda inspired by all the hype around Web 2.0 and the cool features AJAX technologies allows you to do on a webpage.
It's really fascinating the way the web is moving from pages with information towards applications with communication.
To try out the technology we setup two identical search & result pages, that searches on a mondosearch which have indexed www.itu.dk. One of them we did our best to AJAX enable (narrowing search results on the fly, no full post-backs, scrollbar navigation).
Check out the samples here. If you have difficulty sleeping and feel like reading the end report, download it from here.
Later on I've been quite interested in all the possibilities there is in using AJAX along with data from user behavior to improve search - one example could be a feature like an autocomplete drop-down in the search field that suggests commonly searched queries (yes I do realize that this feature has gotten quite popular several places after Google introduced Google Suggest).
The end conclusion of our report? We kind of agree that AJAX is definetly a cool technology that can help extend the functionalities on current old-tech html pages....But the downside is that it's ugly as hell - using tons of different technologies to interact in a spider-web-chaos. Whats really needed is a new web-architecture thats intended for this use and thoroughly designed - not a big rag of patchwork upon patchwork.
This being said, I still won't hesitate to use AJAX to spice up my web-applications in the future.