I've installed Ubuntu 14.04 as a Hyper V client, although I don't often reboot my VMs (I would have to check if other VMs exhibit this behavior), whenever I 'reboot, shutdown, or turn off'. It takes approximately 20+ minutes to complete the process. I am fully up2date including drivers. I've read a few articles, there is a hotfix http://support.microsoft.com/kb/2823643 that doesn't appear to apply to my version of Windows Server. I am not quite sure how to diagnose this issue? It's a nuisance when you are doing administrative work and have to wait 60 minutes (in total) for each reboot process to complete.
Regards,
Horace