I just upgraded my first Xen guest to the latest 5.2 kernel (2.6.18- 92.1.13.el5xen) and got a kernel error on reboot:

powernow-k8: BIOS error - no PSB or ACPI _PSS objects

No problems seen yet. I would think that the guest should not try to do any powernow stuff at all. Has anyone else noticed this?

Kai