We found this old list on Techrepulic  by Rick Vanover and thought we would go through and freshen it up and add our perspective because technology moves quick and things change sometimes day to day. We are now on item #2.

Rick Says

#2: Storage and networking will be your biggest pain points

Planning a server virtualization implementation of any scale will require a lot of planning in the areas of storage and networking. In a server virtualization strategy, the migration from local storage to shared centralized storage takes adequate sizing and planning. Further, administrators will be challenged to rethink the provisioning of virtual servers.

From our experience Rick is dead on.  We have done hundreds of deployments in Education, Corporate, Wndows, Novell and Mac environments and going to a centralized storage solution allows our customers better performance, productivity and manageability but it makes the administrator rethink how they support their end users.  The planning portion of this process is vital and collaborative as it allows the Administrator to fully comprehend the reach of virtualization and the indirect and the direct savings while we customize the best solution.