Looks like Microsoft has released an update for Windows Server 2008 Hyper-V so that it can work more efficiently with Linux guest OSes.
A set of drivers that enable synthetic device support in supported Linux virtual machines under Hyper-V.
Driver support for synthetic devices: The Linux integration components include support for both the synthetic network controller and synthetic storage controller that have been developed specifically for Hyper-V. These components take advantage of the new high-speed bus, VMBus, which was developed for Hyper-V.
Hypercall adapter: The Hypercall adapter is a thin layer of software that translates the Xen-specific virtualization function calls from a Xen-enabled Linux kernel to Microsoft Hyper-V hypercalls. This results in improved performance for the Linux virtual machine.
Fastpath Boot Support: Boot devices now take advantage of the storage VSC to provide enhanced performance.