Linux Virtulization Options (or to KVM or not to KVM?).

[Mick T]

I'm in the process of replacing a few older servers, and I think this
would be a good opportunity to take advantage of virtualization to save
on hardware and related costs. Both Red Hat and Ubuntu are moving to
using KVM for their virtualization choice. I'm leaning towards using
Ubuntu with KVM as a host for both Linux and Windows 2003 server guests.
My google-fu hasn't turned much information about the performance of
guests, nor many hints of large scale implementations.

Has anyone used KVM with both Linux and Windows guests and would like to
share their experiences or advise? 

I'm interested in how stable KVM is, and how well guest OS's perform
under KVM. And if anyone has done any (or come across any) performance
comparisons between KVM and VMWare and any other virtualization
technologies? 

Plus, how easy is it to use? I want to make sure that less-experienced
folk will be able to manage whatever I build with minimal intervention
from me.

Many Thanks! :)
Mick Timony