VMware outshines Hyper-V, et al. in hypervisor comparison
Excerpt: "XenServer 5 is missing 802.1Q virtual local area network
(VLAN) trunking, and as far as security it does not offer directory
services integration, role-based access controls, or security logging
and auditing or administrative actions."
http://searchservervirtualization.techtarget.com/news/article/0,289142,sid94_gci1349210,00.html?track=sy420