Apparently Tens Complement, the company that was developing ZFS for Mac OS X as a separate product has been acquired by Green Bytes in mid 2012. They've very kindly made a version available to everyone for free. There's no UI or any other frills, but for those already familiar with ZFS from Solaris, this is a good development.
See http://zevo.getgreenbytes.com/ for more details.
You have to register on their forums first, before you can download the new ZEVO Community Edition