With the introduction of Red Hat Enterprise 6 Beta, Red Hat has changed direction in their choice of virtualization: they have dropped Xen entirely in favor of KVM.
This is not entirely a surprise, since Red Hat bought Qumranet, a company active early on in KVM development.
What does this mean for us as administrators? This means that we will have to convert any Xen virtual machines to KVM machines if there is to be support from Red Hat. Alternately, support for Xen will have to come from Citrix. This means either internal costs (such as labor, downtime, etc.) to migrate from Xen to KVM or external costs in adding Citrix support of Xen to the costs of Red Hat Enterprise Linux.
With this in mind, even if we do not have Xen virtual machines, we need to learn a new virtual environment before we are called on to support it in-house. When the company calls on you to support a KVM virtual machine, you will be ready.