One of the most exciting new virtualization features in Windows Server 2008 R2 (R2) is clearly Live migration. With Live migration you can move running VMs from one Hyper-V physical host to another without any interruption of service. Live migration is part of Windows Server 2008® R2 Hyper-V and Microsoft® Hyper-V Server 2008 R2.
R2 and Hyper-V server R2 are expected to ship early in 2010, the betas are currently available.
Information about Windows Server 2008 R2 Download the beta of R2 Download the beta of Hyper-V server R2 Architecture Overview of Live migration Read a Step-by-Step guide on how to use Live migration
Video demo on TechNet Edge Video demo on YouTube