- my hardware isn't young enough to support native virtualization
- OS virtualization doesn't support mixed environments
- full virtualization tends to bog down on my older equipment (VirtualBox, VMware)
- ESXi is overkill for my hard ware (need a second box for it to be useable)
- KVM is a bit too light
That leaves Xen. I picked up "The Book of Xen" at the recent ShmooCon and have played with the CentOS version enough that I want to try the Debian version and play with DTC-Xen. If it allows access to some of my not-normally-supported-in-VM hardware (and it looks like it will), I'll probably make the switch permanent.