FSM: Virtualization in OpenSolaris16 Oct 2007
The Free Software Magazine has an excellent article by Rami Rosen on Virtualization in OpenSolaris
An interesting thing to note is that Solaris Zones were created in response to FreeBSD jails -- which allow light weight virtualization of the FreeBSD host system.
What isn't mentioned is that Solaris (proprietray) recently announced the capability to fully virtualize linux (Red Hat) and windows guest operating systems.
This is an interesting addition to the existing virtualization heavy weights like Xen and VMWare.