££ plain and simple. Licensing for Windows for us is dirt cheap. We have a 4 node cluster at our main site and a 2 node cluster at our DR site. Switching to MS pretty much paid for 2 of the nodes. We have Datacenter 2008 on all nodes so unlimited VMs
Yes i realise that VMware is streets ahead in lots of areas, and our setup is definitely not as slick as the old Vmware cluster, but i can imagine they will find times tough in a couple of versions time.