While Service Pack 2 contains many fixes that I recommended earlier, I intend to post here some recent fixes that helped in newer situations:
2. The volume GUID may unexpectedly change after a volume is extended on a Windows Server 2008 failover cluster node http://support.microsoft.com/default.aspx?scid=kb;EN-US;970529 , especially important when using SCVMM as well
3. A Hyper-V differencing disk that you create in Windows Server 2008 R2 cannot be used in Windows Server 2008. http://support.microsoft.com/kb/971677/en-us
...to be continued....