ZFS _is_ a work in process in Solaris and of course in FreeBSD too. But it runs quiet well, again I wouldn't try it on a production server whether it's marked experimental or stable. The more people test it now the earlier it will be ready for production.
>So give it time.
But without real world tests it will be never ready and FreeBSD has not got a plethora of users. Pjd cannot do it all alone, he can do a thorough port, but the users are for fine-tuning.
>They've had 10+ years to get things to this point.
And as a commercial company they did tests on real world machines to iron ZFS, but there is no company which will take this burden for FreeBSD. Ten years to mature as filesystem per se, it doesn't need another ten years for a "mere" port ;-)
http://wiki.freebsd.org/ZFSKnownProblems
http://wiki.freebsd.org/ZFSTuningGuide
http://wiki.freebsd.org/ZFS