I happen to view this question. I have deployed Xen virtual machines across lots of servers in our cluster. The platform is Fedora 12. We have done lots of tests on it and plenty of computation is done on these VMs. It's quite stable. The only pain is that you need to compile the kernel by yourself:
http://fclose.com/b/1535/setting-up-xen-pvops-dom0-on-fedora-xen-3-4-2-kernel-2-6-31-with-paravirt_ops-in-fedora-12/
