IDC study, titled "Worldwide virtual machine Software 2005 Vendor Shares" is summarized at Tekrati, Some excerpts:

The worldwide virtual machine software (VMS) market grew to $560 million in 2005, a robust 67 percent growth over the previous year and topping the 63 percent year-over-year growth recorded in 2004, according to IDC. EMC/VMware was the top VMS vendor in 2005, with a market share of over 55 percent.

John Humphreys, research director for IDC's Enterprise Computing group. "While we believe VMS is a foundational technology to the creation of dynamic IT environments, the challenge going forward is to get users to integrate virtualization with legacy management tools and enhance management functionality to solve specific business issues."

Linux experienced the fastest growth

Industry-standard (x86-based) systems lead the market for VMS software

North American organizations purchased over half of all VMS products

New use cases for the technology emerged

Source: 1, 2

Prashanth Rai