Hat's off to VMware for its leadership in server virtualization. That said, I am hearing more and more stories about heterogeneous server virtualization in large organizations. Does this mean that VMware is faltering? No. As virtualization has gone from cutting edge to mainstream however, IT organizations are gaining virtualization experience, testing other platforms, and finding good fits for KVM, Microsoft, Oracle, and XenServer -- along side VMware.At the beginning of 2010, ESG Research asked 345 mid-market (i.e. less than 1,000 employees) and enterprise (i.e. more than 1,000 employees) firms which server virtualization solutions were currently deployed at their organization. The data supports the scuttlebutt I heard on my recent travels:VMware Server 38%Microsoft Virtual Server 36%VMware ESX: 32%Citrix XenServer 30%VMware ESXi: 18%Oracle VM 19%Microsoft Hyper-V: 17%Sun xVM Server: 10%KVM: 9%Based on anecdotal evidence, I don't think this is a phase -- it looks like multiple server virtualization platforms in the enterprise is the future. What does this mean?1. Server virtualization will get more complex. IT will need specialization on multiple platforms. 2. Vendors need to pick multiple dance partners. VMware is clearly a safe bet but IT infrastructure and tools vendors need to think beyond VMware alone. Microsoft and Citrix will likely recruit partners with an endpoint focus while KVM and Oracle will be more of a data center play.3. Services opportunities abound. IT complexity and skills deficits are on the horizon. Services vendors that can bridge these gaps will prosper in 2011 and 2012.