ZFS should be your choice today if you need an advanced filesystem on Unix
The other day I ran down why ZFS is your only real choice on Linux if you need an advanced filesystem. Well, it's not just Linux. I don't know enough about the landscape of filesystems on other Unixes to confidently say it's your only choice on non-Linux Unixes, but I do think it is by far your best choice for this job.
Let's start with the first and biggest reason: ZFS works and has for years. At this point ZFS has been running in production environments (some of them very big and/or demanding) for more than half a decade. Yes, development is still happening and people are still finding issues (just as they are with essentially any filesystem), but the bulk of ZFS (in code and features) is extensively battle tested and is highly unlikely to blow up on you. Using ZFS puts you nowhere near the bleeding edge, and I don't think there's any other advanced Unix filesystem that can really make that claim.
The second reason is that ZFS is cross-platform, and in fact with care and advanced planning you can move ZFS pools between Unixes (instead of just shifting from one Unix to another for your next storage server build or the like). Chosing ZFS does not lock you into Solaris the way it once did; these days you can run ZFS reasonably sensibly on your choice of Oracle Solaris, anything Illumos based (eg OmniOS or SmartOS), FreeBSD, and Linux. People are running ZFS in production on all of these. This covers almost all of the gamut of major remaining Unixes and gives you plenty of choices as far as style, administration, user level tools, and so on. And if your first choice of Unix for ZFS turns out to have problems, well, no big deal; you can move your basic architecture to another Unix. In a way you can treat ZFS much the way you treat applications like Apache or Exim and basically host it on the Unix substrate of your choice.
(Yes, yes, the OpenBSD and NetBSD and DragonflyBSD and OS X Server crowds are now annoyed at my over-generalization. Sorry, you're all relatively marginal in this space at this time.)
Finally, and it's high time I said this explicitly, ZFS not merely works but it's decently good and has generally made the right design decisions. I can quibble with some of its architectural choices and it's (still) missing a few features that people continually yearn for, but on the whole it is not merely a filesystem that is there but a filesystem that is actually nice, with choices that are sensible and usable.
This last reason is actually kind of important. If there are no other production ready advanced filesystems on Unixes (Linux or otherwise) then ZFS would win today by default. But if it kind of sucked, you might want to stick with current filesystems and wait unless data integrity was really, really important to you. As it is ZFS is decent and deciding to use ZFS doesn't constrain your Unix choices much, so I think you should seriously consider using ZFS for its data integrity advantages.
(There are any number of situations where using ZFS is still not worth the hassles or the risks. Or to be direct, ZFS is certainly not to the point on Linux and maybe FreeBSD where I think using it is a slam dunk obvious choice. Of course on Solaris or Illumos you basically have no option, so go with the flow.)