At the moment we don't do virtualization on our servers. There is some positive sides to virtualization, especially for server applications, however, we prefer to let the technology mature a little before taking the step. We already have security and disaster recovery solutions in place. And we won't invest in major brand virtualization solutions at this point.
What really interests me at this moment virtually speaking, is the Solaris containers (zones). It offers really good features for complete virtual environments (memory, cpu, disk).
For example you can have a partition let's say /etc that is shared between all your zones. all vm can read the default configuration, but when writing to this partition the virtual layer, create a virtual space in which it stores the modified files for each VM. In other words, All common files in the partition exists only once on disk, and modified files are associed to each VM so that they believe the partition is theirs only. I know that at the moment VMWare prevents even read-only shared partitions, because they believe that their VM should act like real Machines (were one partition cannot be mounted twice at the same time)
I see so many applications to our industry
But Solaris is not the most user friendly OS, for clients and for customization, so we're waiting to see what will come out of all this