Someone will correct me if I'm wrong because I haven't used ZFS-on-Linux (my remaining Linux boxes are slowly being converted to all FreeBSD) but I don't think you can do "/ on ZFS" on Ubuntu since ZFS support is via a loadable kernel module (i.e., it's not in the mainline kernel -- and apparently never will be).

You can install on, e.g., ext4, and then create /home as ZFS and then take advantage of all that ZFS offers (such as sending full/incremental snapshots like this article talks about). Or you could put your databases on ZFS and use snapshots to back them up, and so on.