I found your arctile preface on linuxtoday and wanted to say thank you for writing it. Teaching someone how to do something is hard enough, but to write out the explaintion takes even more skill. I liked your examples on recovery and I can see UML usefull for things like upgrade testing as well. One of the things besides a system boot failure is upgrading to a new version of OS. Which can cause a boot failure or worse total corruption of system and user data. I can see where this could help cut the cost of testing a upgrade scenario. It would require more disk space but not a complete system.For a small company with a producton system this could save a lot.