The virtualization underdog, Microsoft, just released Hyper-V.  This couldn't come at a better time - early.  On the tail of deploying a production ESX server, I need to turn around and deploy a hypervisor HA cluster solution as a proof-of-concept development environment. -- The MS partner program reduces the cost of a Microsoft solution, compared to a baremetal VMWare option, and, with official support of Hyper-V, I'd say the risk has been reduced as well.  Honestly, I don't know if I'd deploy Hyper-V in production today, but given some of the VMotion horror stories I've heard from a "popular hosting provider" engineer, it's hard to have warm-fuzzies with any entry-level HA virtualization product these days.