Here is a quick round-up of post-SP1 hotfixes that it is good to know about, if you are running Hyper-V – I have summarized the file(s) updated and their version details for quick reference so you can see if they are applicable for you.
Hvax64.exe 6.1.7601.17579 (SP1 GDR)
Hvboot.sys 6.1.7601.17579 (SP1 GDR)
Hvix64.exe 6.1.7601.17579 (SP1 GDR)
Hvax64.exe 6.1.7601.21683 (SP1 LDR)
Hvboot.sys 6.1.7601.21683 (SP1 LDR)
Hvix64.exe 6.1.7601.21683 (SP1 LDR)
Hyper-v_model.ps1 (dated 2011-01-13)
Stop error 0x0000007a occurs on a virtual machine that is running on a Windows Server 2008 R2-based failover cluster with a cluster shared volume, and the state of the CSV is switched to redirected access
Csvfilter.sys 6.1.7601.21639 (SP1 LDR)
Clussvc.exe 6.1.7601.21639 (SP1 LDR)
Vmms.exe 6.1.7601.21642 (SP1 LDR)
Also, the Microsoft iSCSI Software Target is now a free download – see this Virtualization Blog post for details.