From checking the forums it appears that yes, I should be able to migrate KVM virtual machines I am currently running on a Proxmox 1.9 system to one running version 3.1 and simply reload them. (Thankfully I have a backup physical host so I can install 3.1, migrate the VMs, then upgrade the main host.) However, one knowledgable poster doing the same thing has said he first migrated to a ProxMox 2.3 server, then from there to 3.1 .... wondering if that middle step is really necessary, and/or if there are any other "gotchas" that would make my 1.9 VMs unhappy if I simply unpacked and ran them on 3.1.