The "Ask the Core team", hosted on the TechNet domain, posted about the top issues they see with Hyper-V.
Check it out: Top Issues for Microsoft Support for Windows Server 2008 Hyper-V
Read the complete post at http://wmug.co.uk/blogs/r0b/archive/2008/12/27/top-issues-for-microsoft-support-for-windows-server-2008-hyper-v.aspx