Quoting from Ask Dr. Root blog:
Consolidating with Solaris Containers:
Solaris Containers combine operating system partitioning with fine-grained resource controls to allow servers to be partitioned at sub-CPU granularity without having to replicate the operating system image itself. They provide a virtualised Solaris 10 Operating System image including a unique root file system, a shared read-only set of system executables and libraries, and whatever resources the root administrator assigns to the container at creation time. Solaris containers can be booted and shut down just like any instance of the Solaris 10 OS, and rebooted in seconds if the need arises. Unlike virtual machines, which must intercept every single interrupt and allocate it to the right instance, Solaris Containers support mainframe-level partitioning capabilities with almost zero overhead.
Consolidating using VMware ESX Server :
When an IT organization wishes to consolidate multiple Linux applications, multiple Microsoft Windows applications, Solaris OS applications, or a combination of them all, ESX Server is the consolidation option of choice. Not only can its virtual machine technology support all operating systems, it can support multiple versions of each one as well. IT organizations consolidating onto Sun x64 servers running ESX Server have the additional benefit of migration software that helps to package up an entire environment so that it can be installed in its own virtual machine.