ZFS allows you to do a snapshot before an upgrade. If the upgrade breaks something, you can just reboot into GRUB and choose which snapshot you want to boot into. So you choose to boot into an earlier, functioning snapshot, and then destroy the latest broken snapshot. This takes a few seconds. This is another killer feature that Solaris has; it is the combination of ZFS + Snapshot + GRUB that gives this unique power called Boot Environments. If you think that "ZFS allows you to do snapshots, wow" - you have missed the point of BEs. If you upgrade your Linux installation and break it, what do you do? Reinstall everything? How much downtime? With BE + ZFS you have only a minute of downtime.
Again, it is the combinations of different techniques that give the power. It is said that Unix is simple, but there are pipes, etc that allow you to combine different single commands giving you the power of Unix. Each command in itself might be nothing special, but the combo gives you real power. If you dont understand why, then it is your loss. Same with Solaris. Containers in itself is not that powerful, it is the combinations of Containers + ZFS + Crossbow and other combos.