From the Mac OS Forge project page:
The ZFS project has been discontinued. The mailing list and repository will also be removed shortly.
Snow Leopard dropping support for ZFS was the first sign that the project wasn’t going very well. But, now it’s official, the project has been canceled.
John Gruber, of Daring Fireball, has heard that the decision was a legal one. The nail in the coffin was either the CDDL license, Oracle’s acquisition of Sun Microsystems, or the NetApp patent lawsuit against ZFS.
Nearly everyone “in the know” was excited about ZFS, it was a truly revolutionary file system, but I’m excited to see where Apple goes from here. Especially since Apple is working on their own next-generation file system.
Update 10/25/09: Jeff Bonwick, lead developer of ZFS at Sun, has confirmed that Apple abandoned ZFS over licensing issues.