Ubuntu Server 12.04.3 / 12.10 / 13.04 / 13.10 with encrypted md mirrored rootfs and remote ssh unlock
My original plan was to boot from ZFS, but combining it with encryption and especially with mirrored disks turned out to be too troublesome. Yes, I did get it working and booting, but resulting configuration required manual fixing each time new kernel was installed. And don't even think about doing upgrade to next Ubuntu version.