There are many updates for SCVMM and Hyper-V. Some are required just following product install, others are provided to offer greater functionality. Some updates/hotfixes address issues that may constitute a headache for you down the road. I'll list everything I know and provide recommendations. This post will change over time as new updates and issues arise. If you find a hotfix or update that you think should be posted here, please let me know. Include the environment conditions (Windows version, etc) and what the update addresses. Here's to being proactive!
A – Required by product to operate correctly
B – Resolves known issues
C – Adds Functionality
JJ – Get it. This is on my short list when working with customers.
A – SCVMM – Hyper-V
956589 Description of the Hyper-V update for issues that may occur when you manage the Hyper-V role on the 64-bit editions of Windows Server 2008 by using SCVMM
A – SCVMM | BITS
956774 A Background Intelligent Transfer Service (BITS) client cannot handle files that have paths that contain the volume GUID in Windows Server 2008 or in Windows Vista
B – JJ – SCVMM | WMI
958124 A wmiprvse.exe process may leak memory when a WMI notification query is used heavily on a Windows Server 2008-based or Windows Vista-based computer
B – JJ – SCVMM | WMI
954563 Memory corruption may occur with the Windows Management Instrumentation (WMI) service on a computer that is running Windows Server 2008 or Windows Vista Service Pack 1
B – JJ – SCVMM - WMI
955805 Certain applications become very slow on a Windows Server 2008-based or Windows Vista SP1-based computer when a certificate with SIA extension is installed
B – JJ – SCVMM | P2V
959596 Description of the System Center Virtual Machine Manager 2008 update to address physical to virtual (P2V) issues
B – JJ – Hyper-V | VSS
956697 Windows Server 2008 Hyper-V VSS writer is not used during a backup job because of corrupted or invalid virtual machine configuration files
B – Hyper-V | VSS
959978 Error message when you back up a Windows Server 2003-based virtual machine on a Windows Server 2008 Hyper-V-based computer: "GetWriterStatus FAILED for Selected writer [Microsoft Hyper-V VSS Writer], writer is in state  [VSS_WS_FAILED_AT_FREEZE]"
B – Hyper-V |SCVMM
957967 Stop error message on a Windows Server 2008-based computer that has the Hyper-V role installed: "STOP 0x0000001A"
B – Cluster | Hyper-V
957311 Recommended hotfixes for Windows Server 2008-based server clusters
B – JJ - Hyper-V | Drive Letters
958184 Virtual machine backup operations fail in Windows Server 2008 when Hyper-V virtual machine files are saved on a volume that is mounted on a failover cluster by using a volume GUID
B – Hyper-V | Cluster
958065 You cannot configure a Hyper-V virtual machine by using Windows Server 2008 Failover Clustering when the virtual machine uses a storage device that is managed by a third-party clustered file system or a third-party replication solution
C – Hyper-V | Cluster
951308 Increased functionality and virtual machine control in the Windows Server 2008 Failover Cluster Management console for the Hyper-V role