a4j:commandButton works fine for me in both IE 8 and IE 9. Could you please provide more information?
working fine for me as well in IE8 richfaces 3.3.3 final tomcat 6.
I really do not understand why it did not work, but it works now.
Problem was that when a page was opened, "ajax action" on the server side worked but the page was not refreshed. Then you clicked F5 button to refresh the current page and then call ajax again, it worked.
Using RichFaces 3.3.3-final with IE 8.0.7601.17514, Windows 7 64bit