If you are running Windows Failover Clustering and Hyper-V then this patch might apply to your environment.

With this hotfix we increase functionality and add more control to Hyper-V virtual machines running in a clustered environment. Here are some of the improvements:

• Changes to the virtual machine view: additional actions like start, shutdown and turnoff added.
  
• Allow for more than one virtual machine in a "Services or Applications" group: This is one of the important updates, we will now let you add/select multiple virtual machines in High Availability (HA)wizard. The wizard will detect if there are multiple VM’s that have files on the same clustered disk. If it is the case they will be enabled and configured for HA
  
• Add support for mount points or volumes without a drive letter: The High Availability Wizard can detect when files for a virtual machine are on a volume that is using a mount point or a GUID instead of a drive letter. Additionally, the High Availability Wizard moves the appropriate disks into the same Service or Application group as the virtual machine resource.
  
• Behavior change when you add a pass-through disk to a virtual machine: The Failover Cluster Management console correctly shows that the configuration change is not successful.
  
• Volume path copy
  This update lets the path of a storage volume to be copied from the properties of the disk resource in the Failover Cluster Manager console. When you configure a virtual machine, the paths of the volumes must be specified for the disks that will be used. After you apply this update, the path can be copied from the properties of the disk in the Failover Cluster Manager console. This is useful when the path is very long, such as when a volume uses a GUID instead of a drive letter.

This hotfix will help a lot of our customers who are deploying Hyper-V in a Windows Failover cluster environment. Read the full list of improvements: http://support.microsoft.com/?id=951308

At least I could help one customer today :)