Several people i know run ZFS very successfully on Funtoo Linux. Funtoo being a Gentoo-Fork lead by Daniel Robbins himself.

--- http://www.funtoo.org/ZFS_Fun

--- http://www.funtoo.org/wiki/ZFS_Install_Guide

I personally haven't used it so far, but i hear good things :)

I agree with your statement though: ZFS + Jails is a killer pro-BSD argument when it comes to servers.