I see a trend happening here. The next version of WebWork, as well as Tapestry and JSF are all embracing Ajax technologies. By "embracing", I mean they're not only using them, but they're making it easier for us to use them.
After using XmlHttpRequest in my last two projects, I think this is a must for Struts and Spring MVC as well. The technology is very cool and customers absolutely love it.
The question is how do we bake it in? WebWork makes it easy because its tag libraries are backed by customizable Velocity templates. With Struts and Spring MVC, it seems the best way would be to use tag libraries, but maybe there's better alternatives. Do they each need an AjaxAction/AjaxController or something that allows DWR-type stuff?
What are your thoughts? You might argue that using DWR should suffice, but w/ everyone else (even Rails) baking it into the framework - I see no reason why Spring MVC and Struts shouldn't do the same. You are using these frameworks to develop kick-ass UIs aren't you?