When properly implemented and managed, virtualization means cost savings -- for server hardware, support and administration -- as well as easier server deployment and reduced energy consumption. But for these benefits to come fully to fruition, the virtualization layer of the stack has to be managed independently of either the application or the physical server.
Fortunately, that's not difficult if you do it right.
Sure, server provisioning and back-up become easier in the virtual world. But monitoring, especially checking the servers' underlying physical resources, becomes even more important. You have to balance the types and numbers of virtualized applications among the physical servers with an eye to best use of resources.
The consequences of getting it wrong can turn some -- or all -- of the virtualized applications running on a physical server into poorly performing slugs.