Nvidia recently released their SLI Multi-OS:
"With the introduction of NVIDIA® SLI® Multi-OS technology, a user now has the ability to fully virtualize all resources in the workstation, including NVIDIA® Quadro® GPUs. An SLI Multi-OS enabled workstation operates in conjunction with workstation virtualization software. Through SLI Multi-OS technology, a user can directly assign a dedicated Quadro graphics board to both the host operating system and a range of optionally loaded guest operating systems." --- NVidia.