Dr Who references aside, there is an interesting debate forming over implementing virtualization with containers instead of hypervisors. Many application servers use the container model and while there are some benefits I don't know that I agree about the concept of delivering more services. There is much duplication in the container model and hypervisors try to reduce that since it is essentially wasteful. Some of the problems with hypervisors, such as hoggy neighbors and "cpu stealing" are not addressed with the container approach.
Link: Containers vs Hypervisors