An old Comparison...  Microsoft Hyper-V R2 pros   Microsoft Hyper-V R2 cons  Anything I miss to Add?
According to this article, the installation base market share for major vendors:  VMWare        65% Microsoft        27% Citrix/Redhat  8%  Also, it looks like KVM is picking up in a very fast pace.   [URL]
Microsoft, Others Closing In On VMware In Server Virtualization Market