ZFS is Sun's latest filesystem (which is open source). I have been personally watching ZFS from afar ever since I read their presentation slides on the thing. It is rather impressive. Plus I always support people taking a stab and trying something new out, especially when it is to help us move forward in the UNIX world instead of being stuck in the past.
But what triggered this post is that it looks like the ZFS is being added to OS X 10.5. That makes me a happy boy.