I got around to setting up a new yum repository to store my activemq rpms.
You can find it at http://packages.platform14.net/repo/activemq/. Currently I've got RHEL/Centos5 packages there. I'll put up a koji instance there soon and add Fedora13/Fedora14 package too. they all build out of my github repository : https://github.com/jamesc/apache-activemq
To enable, here's a .repo file:
It currently contains the latest 5.4.2 RPMS.