from http://www.heise.de/english/newsticker/ ... from/rss09

"KVM, which was presented to the public only barely two months ago,
thereby easily overtakes other virtualization solutions such as Xen,
OpenVZ and Vserver, which are based on other approaches, on the
path toward integration into the kernel. Xen, for example, has been
hoping in vain to make that leap for almost two years now. With the
likewise accession to 2.6.20 of the hypervisor interface the chances
of Xen at least of finally approaching the Linux kernel are likely to go
up once the environment builds on the new interface."

KVM only works with very modern CPUs, though. Xen works on older stuff that doesn't have the CPU support for virtualization.