I have developed an application in JBoss Seam 2.2.1.Final using RichFaces 3.3.3.Final. Some parts of the code make heavy use of a4j calls, i.e. Ajax calls. This works very well under most browsers. Unfortunately when IE9 was released two weeks ago, it refused to work with my application. I would click on certain links and nothing would happen. Or I'd get blank pages back.
Eventually I traced the issue to a known bug in the Sarissa.js file that is used by RichFaces for XML and DOM parsing. This file in RichFaces 3.3.3.Final is not compatible with IE9.
A couple of changes to the file made it work for me on my site however. The attached file can be used in your project and just reference it so that it overrides the built in one.