Generally, IT managers said they don't need as many server administrators -- or as many server boxes -- to run virtual servers. In addition, Congdon said Capitol One has used the technology to grow into more of a full-service bank faster, moving beyond its image as a credit card company. He explained that financial applications used by newer business units can be added to a collective of servers, instead of relying on the old, more expensive philosophy that every new application deserves its own server, Congdon said.

With the older system, provisioning a new server would take up to eight weeks; it now takes just two weeks, Congdon said. That reduction has made it possible to support faster application development cycles, something the bank needs as it grows.

Congdon said "any" application, mission-critical or not, can be considered viable for running on a virtual server. Some analysts have noted that server virtualization is most often used for more routine tasks not vital to an organization.

Capitol One is also evaluating the use of open-source virtualization, although he would not name any particular software. How it performs in tests will determine whether it is used, he said.

Detroit Medical Center, with nine hospitals in Detroit, has been using virtualization software for three years and expects to expand beyond the 20 servers now sharing up to four virtual servers apiece, said John Karras, director of technical services at the center. So far, the virtualization process has yielded a 40% increase in servers without requiring more server administrators, he said.