Argh! The company that I work for has just rejected KVM, libvirt and virt-manager because there is no snapshot feature (they went for VMware ESXi instead). I was hoping that convirt would have proper snapshots (like VirtualBox and ESXi) but is appears this is actually just a memory dump feature like virt-manager.
Dumping the memory but not the disk state is bad - if you ever restore from the same memory dump more than once and do anything that causes a write to the disk the filesystem will be corrupted. How can it be that two completely different KVM frontends both implement the same incomplete and dangerous "snapshot" behaviour? Snapshotting a VM should save the complete VM state, not just the memory.