[CentOS] xen vs kvm for virtualization on centos/rhel?

> Fedora 13 does save the guest on shutdown so I would expect this will be
> supported in RHEL6/CentOS 6 too. But when do you actually power down a
> RHEL/CentOS server? And if you did, wouldn't you have migrated the
> guests to another box already?
>
mainly it is an issue for a quick reboot of the host for a kernel 
update.  i guess migration is an option for that as well, but not 
everyone has that much hardware.