This is a good question. In an ideal environment, administrators would be able to quickly and easily move workloads between virtual and physical systems with little or no downtime. While I think the marketplace will certainly get there, the process isn't yet 100% reliable. Among the products that perform conversions are VMware Converter, Microsoft System Center Virtual Machine Manager, PlateSpin PowerConvert, LeoStream P>V Direct, Vizioncore esxMigrator and backup solutions from companies such as Symantec. As you discovered some of these tools are only designed to work in one direction, such as VMware Converter being primarily used to migrate workloads to ESX Server.
From a technical standpoint, conversion utilities need to strip out any hardware-dependent portions of the guest OS. Device drivers, the Hardware Abstraction Layer (HAL) and OS configuration settings can vary and must be managed by P2V tools. The task can be tricky and is often OS-specific, but necessary, for P2V, V2P, V2V and image-based conversions. Of the products I mentioned, I recommend you take a look at PlateSpin PowerConvert and their hardware-independent image-based approach to workload portability. As long as your Guest OS is supported, it should allow you to move entire VMs to physical machines. Of course, you should be sure to thoroughly test any converted system prior to deploying it into a production environment. I hope this is helpful, good luck!
This was first published in February 2008