Something I've been keeping an eye on for awhile: ZFS for Mac. It was supposed to be included in Leopard (IIRC) but was cancelled; rights issues, if I'm not mistaken.
Well, the guy who was in charge of that project has struck out on his own and just recently released it as
Zevo.
Why I'm interested: my grandmother has a MacBook Pro, and uses it to put together family movies. The source files are spread across a half-dozen or so external hard drives. There's some redundancy across drives, but not really any kind of reliable backup. The drives themselves are probably a decade old and mostly full.
A few years back she bought my old roomie's rack of external LaCie drives, but I realized in short order that they weren't going to be a vastly superior solution as-is (3 500GB drives and 1 1TB drive, arranged in a software RAID -- simple concatenation IIRC, not striped or mirrored) -- they didn't have enough space to replace her existing bunch of drives, and there was no redundancy so they weren't reliable.
So I replaced the 4 drives with new 2TB ones. I thought of doing a RAID10 thing, but saw Zevo was under development and decided we could wait.
Well, looks like the sucker's finally been released -- partially. They're releasing it in Silver, Gold, and Platinum Editions (in pizza-franchise-style they-think-we're-stupid inflation -- if you have three sizes, the smallest one is not a MEDIUM, asshole) and so far only the Silver is available. The good news is they're offering to let you upgrade to each successive version as it comes out, for just the price difference; the bad news is that it still doesn't look like Silver (or even Gold) has the full feature set I want (RAID-Z), so I'll have to wait anyway.
Still, neat.