remember. It is only concerned with /usr and to as minimal a degree
as possible /etc. People likely still want snapshot and rollback for
their actual _data_ as well.
(Choosing a random point in the conversation...)
I'm starting to think that snapshots are never the right tool, at best a local optimization:
For the OS and application code and static data: What we really want is the ability to reinstall/redeploy this data if it became lost or corrupted. We don't really want point-in-time snapshots; snapshots are only a local optimization allowing us to "redeploy the version that has been installed yesterday". An ideal technology would allow "instant" deployment of both old and new versions (redeploying and old version and deploying a new version have structurally the same effect on a filesystem), then snapshots wouldn't be needed.
For users' data: What we really want is backups—definitely on a different disk, ideally off-site. An ideal technology would allow continuous replication of the data elsewhere. Snaphots are at best a way to quickly access a backup from the past hour, but are not at all a replacement for a backup.
For configuration: What we really want is a VCS, dealing with changesets, documenting who has changed what, when and why. Snapshots are a really poor VCS.
Obviously we don't have all that technology that we "really want", or at least not in a way that is ready to deploy, but we kind of have snapshots. Let's just not think that snapshots are "right".