From the 'some point releases are bigger than others' files:

Red Hat today officially announced the beta availability of Red Hat Enterprise Linux 5.4 (RHEL), which in my view is a lot more than a typical point release. Sure we're all waiting for the big RHEL 6 release, but there are some major changes in RHEL 5.4.

The most obvious change is the shift to the KVM hypervisor (as opposed to Xen). Xen is still in RHEL, but with RHEL 5.4, Red Hat is signaling its intention that KVM (eventually) is to be Red Hat's preferred Hypervisor. It's a preference that Red Hat execs have indicated at multiple points this year and should be no surprise since Red Hat now owns lead KVM vendor Qumranet.

RHEL is Red Hat's flagship platform and the inclusion of KVM is the first really big shift for Red Hat's new virtualization roadmap which favors KVM. Red Hat also has - in private beta - a standalone KVM hypervisor product as well as new server and desktop virtualization management application.

While KVM is the big new item in RHEL 5.4, there are also a few other goodies for users to try out.