The combo of open source and virtual machines is really providing some powerful options for rapid evaluation and prototyping. 

Here is an example … "Want to do some network management?" … then download the $10 PDF of "Network Monitoring with Nagios", then get the VMWARE Player, and then check out the Nagios appliance deployment for VMWARE. 

In a couple of clicks, your up and running and ready to do some network management.  If you like what you see, a couple of file transfers, and some more clicks, and you can be in production mode. Nice.

Thanks to a recent HomeNetworkHelp.info podcast for getting my thoughts moving in this direction.