ZFS is really cool. The best things that stood out out to me when I researched it a bit a while ago (though there is so much cool about it) are
1) more storage than you could ever possibly use–you won't run out. 2) you can add and remove drives on the fly. 3) you don't have drives you mount, you have pools you can add to and remove from (on the fly). 4) great redundancy/error-checking built in, in all forms.
The best feature is that you can tell it to do a "zpool scrub poolname" and it will go through the entire set of drives in that pool and check the checksums, correcting as necessary. Given that there are errors that can occur silently, ZFS can detect and correct them if they are single-bit errors.
1) more storage than you could ever possibly use–you won't run out. 2) you can add and remove drives on the fly. 3) you don't have drives you mount, you have pools you can add to and remove from (on the fly). 4) great redundancy/error-checking built in, in all forms.
I'd love to see it on the Mac, officially…