I am also a VMWare fan and was very happy when they released VMWare server for free a while back. I use VMware Server every day to run a Windows XP machine and Ubuntu Server in a virtual networked environment which I develop client/server apps on. It works awesome.. although I long for faster hardware emulation.

I'm rooting for KVM to take over, however it probally needs some time to settle down. Networking is harder to setup, and I've noticed graphical glitches in winXP.