Gartner published it’s annual overview of server virtualization solutions in it’s 2012 Magic Quadrant for x86 Server Virtualization Infrastructure publication. The publication has a good overview of the position of the solutions in the market.
Hyper-V moved a bit closer to VMware vSphere since the 2011 Magic Quadrant while Gartner based the 2012 Magic Quadrant on Windows Server 2008 R2 SP1 and System Center 2008 R2 SP1. See the Quadrant of 2011 here. Next year when Gartner publishes the Magic Quadrant Microsoft will probably positioned very close to VMware. Hyper-V in Windows Server 2012 has many new features as well as System Center Virtual Machine Manager 2012.
Quote from the Gartner site:
Citrix, Microsoft and VMware remain in the Leaders quadrant in 2012. Microsoft has been improving its overall road map and clarifying its strategy, but still struggling to deal with an entrenched VMware — especially in large enterprises. The functionality gap between VMware and Microsoft for basic x86 server virtualization infrastructure has gradually narrowed, while the pricing gap hasn’t narrowed. Citrix remains a major player, but at this point due entirely to its strength in hosting desktop virtualization workloads, not in the general server virtualization market.