"Next generation virtualization software? Maybe Xen."
When I first heard of the Xen project, I was a bit skeptical of a virtualization solution that required hacking the host O/S kernel, especially when one of the hosts is Windows. That seemed unlikely to prove more than academically interesting, but the Xen team have ported their technology to both open and closed source stacks, and most importantly they've done an excellent job packaging the free version of their project with a RH-based LiveCD, pre-burned Debian image, etc. It suddenly looks like they'll have something worth considering for server consolidation and virtual hosting situations, as well as the grid solutions they initially targetted.
Hopefully they have the same luck that UML and LTSP had getting their kernel hacks rolled back into the Linux source tree.
Other academic virtualization projects via the virtualization wiki