I remember just before Oracle took over Sun, OpenSolaris was a pretty viable desktop machine. They had a feature called "Time Slider" that was built into Nautilus. It was like Apple's Time Machine, only based on ZFS snapshots instead of backups to a separate disk. You could slide a widget back to get to a previous snapshot of the disk. OS upgrades also worked together with ZFS snapshots so that you could atomically roll back to a previous version just before the upgrade took place. It was all really awesome.