M$ is flaunting news of a customer migrating from VMware to Hyper-V virtualization on the server. The subject customer is a M$ shop and sees the major reason to switch being cost… If they were not a M$ shop but working for themselves they would see that KVM or VirtualBox would save them more money by far.
M$ charges only about $20 for Hyper-V as long as you pay them $1000+ for 2008 and the damned CALs.
VirtualBox and KVM cost $0 for the server licence and the hypervisor included. Users of GNU/Linux also save a bundle on re-re-reboots that are killing some in large deployments of that other OS.