SCVMM can now trigger live and quick migration of virtual machines on R2 clusters.
SCVMM can now place multiple VMs on a single LUN configured as a CSV
SCVMM can now use SAN migration mechanisms to move virtual machines in and out of clusters. Multiple LUNs per single iSCSI target are now supported, which lets SCVMM use certain iSCSI products from Network Appliance and EMC.
From 2008 R2 comes support for Virtual Machine Queues (VMQs) & Chimney (TCP offload engines). VMQs are a mechanism for the network cards to transfer data via DMA directly into the child partition's memory. Also, different processors can serve different queues, thus enhancing scalability greatly. For more details, see http://msdn.microsoft.com/en-us/library/dd434877.aspx
Maintenance mode is supported across all platforms: Hyper-V, VS and VMWare ESX hosts. Putting a host in maintenance mode triggers live migration (where possible) of all VMs on the host on Windows 2008 R2 and VMWare. Also,migrations for performance and resource optimization (PRO) to the host are disabled.