Every company I have worked for has decided to outsource their datacenter to a managed hosting provider, in some manner or another. Some only outsourced their websites, others went all in and had them manage their entire infrastructure.
Most managed hosting providers will regulate everything from the operating system down the stack to the hardware, the cooling and the electrical for you. Many will use virtualization technology of some kind to help optimize usage and resources for you. They even help companies "right size" their virtualization environment when it goes into their hosting environment.