I tend to see XEN where the PERFORMANCE of the OS instance is the primary concern or where there are limited funds for the virtualization software. Mostly schools and medium sized business.
Interestingly, though I’m not sure of the impact, I see more hosting companies leaving VMware and migrating to Virtuozzo or XEN.
Could be. I'm using VMware both as an individual, and as the System Admin for a small (<100 users) company where VMs are running on our servers and on our users' notebooks. I'm aware that there are big companies doing huge VM hosting applications; that's not my bag at present.
I seem to remember Xen having the ability to do effectively instant migration from one physical host to another over the network without a noticeable loss of service. That's a serious enterprise feature. Does VMWare have this?