Today this blog post http://virtualsimon.com/wp/?p=24 about moving VMs between XenServer pools completely saved my bacon. Also see http://support.citrix.com/article/CTX121282 for more info on backing up and restoring VM metadata. Should also say that something tells me that this is a lot more robust on KVM. This is the secret sauce for moving VMs between pools with the free product. Without doing this, your Windows systems will boot to a blue screen 7b.