I have worked on AJAXTags a bit. The newer AJAXTags version 1.3 has removed its integration with Struts, but you can always write your own simple Struts Action which is very well supported.
But again, there could be certain roadblocks like setting Request Attributes, which even the Action class wont be able to set, although there may be no errors while trying to set. [Just 4 knowledge] But you can always have various work-arounds to it.
I think its a nice framework keeping in mind the usage of interfaces like tabpanels, autocomplete select, portlets, etc.
That is a really big piece of pie for such a tiny ad:
Building a Better World in your Backyard by Paul Wheaton and Shawn Klassen-Koop