Do you use GWT?
Though I have not used it , but whatever I know about it from that I can say that developing a AJAX based web application would definitely be much easier using GWT.
Think about it.One is a java
programmer and familiar with java.He can make the whole application using Java and then GWT would generate the required HTML and JS for this application.Simply host those to see the results.
On the other hand , if we try developing the same AJAX application using js library like prototype.js then we can make out the benefits of GWT. Ulf : The good folks at Google are going to come after you for that one. :-)
Sorry , its google web toolkit.
The whole intension was to let the original poster know about this option for evaluation.