i too am both curious as to the motivations for VM and completely open
minded with no preconceived notions about VM. except my aversion to
hype.  but hype is independent from the quality of an idea.

i was asking Friday here at work, what are the modivations behind VM?
the only answers that were offered were variations on the ability to
rent someone a machine that has root access without having as many
machines are renters.  the earliest VM i know of is VM/CMS, from IBM,
which is still used today.  its purpose was to provide early
timesharing, and was also used to debug MVS.  so those are two
motivation, although Xen can't be used for debugging OSes since it's a
paravirtual machine.  i don't think VMware would be too good either
because it rewrites parts of your code.  maybe that's not a problem in
practice.

maybe Ron can give us insight into the motivations for using VM.