I wanted to point out that although I am anxiously awaiting support for Hyper-V 3.0, no Citrix products currently support it. Take a look at the hypervisor support matrix for an at a glance view for XenDesktop, or eDocs System Requirements for XenApp 6.5.
:Edit 7/14/2013:
For Server 2012 / Hyper-V 3.0 support, use XenDesktop 7.