It's maturing rapidly and has proven to be very stable so far. We're not using it by default everywhere, at least not yet, and building out an AMI that uses ZFS

It's maturing rapidly and has proven to be very stable so far. We're not using it by default everywhere, at least not yet, and building out an AMI that uses ZFS for the rootfs is still a bit of a research project - but we have been using it to do RAID0 striping of ephemeral drives for a year or two on a number of workloads.