As more enterprises have to manage multiple hypervisor platforms, having a single console to manage the most important parts becomes a real asset to the virtualization admin. For instance, VMware will support Microsoft Hyper-V inside vCenter.
But, what about people that have XenServer in their environment as well? Are they stuck with XenCenter? As it turns out, they are not. Microsoft System Center Virtual Machine Manager (SCVMM) can manage XenServer environments as well (I highly doubt VMware will do this with vCenter). Shane Kleinert has started a multi-part blog series that details exactly how to setup XenServer with SCVMM as well as the reasons you would want to do this.
I highly recommend keeping up with this series if you have Citrix XenServers in your environment.