ARGGGGGGHHGHGHH! I just snapped. The amount of misunderstanding and misinformation in this thread is astounding. I shouldn't be surprised I suppose, I'm not that new here.
People are comparing totally different products throughout this discussion. The worst was: XenServer versus VMware Fusion. "Vmware can run OSX". Oh really? I specialized VMware desktop product can run OSX, while XenServer can't? Well guess what, neither can VMware ESX.
Folks, the comparable products here are VMware ESX (and/or ESXi) and XenServer. These are their respective companies' enterprise offerings, the main designator being running on BARE METAL. Other products like VMware Server, Fusion, VirtualBox, are all hosted (run on top of an operating system). Whether they work well or not doesn't matter for the bulk of this discussion.