AJAX plays well with others and Struts is no different than any
servlet, so
you should be OK. The question that I am having is the whole MVC paradigm which is in a way changed by AJAX. You can have multiple AJAX components in the same page and there is very little that these can do to notify each other of their states. So, it is not like Flex where components are aware of their neighbor's states and can change accordingly. In AJAX this kind of behavior will have to be maintained manually, which is not so easy.
Another thing to consider is the notion of user interface state as a whole. AJAX will not help in maintaing this, on the client. You can try to keep in on the server, but then you'll have memory issues.
Lastly, there is the issue of cross-browser JS compatibility. In a recent project we had to spend considerable amount of time making an AJAX app work well in IE and Firefox.
