Like many sys admins I have used VMWare Workstation to test and deploy new environments and OS. I am starting to use VMWare server in production environments. My current employer is a private university and we have a large amount of individual labs that we support the web sites. In the past we had used one Apache server to handle all the labs. This has become problematic, mainly in the area of stability and security, where one labs script would bring down the entire server.
We have now deployed a VMWare Server that runs on a native Linux 2.6 environment. Each lab gets a virtual server that contains their own virtual machine with a default copy of Apache. We are still in the early stages and have not worked out the details on how many virtuals are most efficient per each server, nor have we work on HA solutions.