I just spent some time talking with Zill from
http://www.zill.net/ who has good experiences with Solaris Zones (processor hit for Zones is apparently around ~1-5% and there are excellent automation tools). As much as I like the sound of Solaris Zones, I still tend towards a solution that is more likely to get used by others and provide more flexibility long term.
I think Cathy is using User Mode Linux. I have ruled out UML based on research and problems getting a testing environment up.
Getting a test version of Xen running was simple ( http://www.cl.cam.ac.uk/Research/SRG/netos/xen/downloads.html ). In fact I had the Xen Demo up and running before I finished reading through the license and downloading the second Solaris 10 CD from Sun (iirc there where ~6).
