Microsoft System Center Virtual Machine Manager 2008 R2 SP1 RC has been finalized and deemed ready for public testing.
"Starting with early December 2010, customers running SCVMM 2008 R2 are able to take SP1 RC out for a spin. You can use this SP1 RC to upgrade from 2008 R2 and you will be able to upgrade from this SP1 RC to the SP1 RTM."
It's being uploaded to Microsoft Connect. Since this is a pre-release version, usage of this is limited to test environments.
Note: Customers should obviously not deploy SC VMM 2008 R2 SP1 RC into production, despite the RC label. However, they need to get ready for the RTM of the service pack, and they can do this by grabbing the SP1 RC bits from Connect and start testing.
More Info: Microsoft Connect