It went nowhere. Linux distros and the mainline kernel are using btrfs, which has a similar layer-spanning design as zfs but is btree based like Reiser (which should make it faster).

Most features are done and you can install with btrfs out of the box today in the RHEL 6 or Centos 6 betas.

http://en.wikipedia.org/wiki/Btrfs

ZFS has the following that BTRFS doesn't * Deduplication - Huge in any virtualization environment * Cache layer - Required for high IOPS * fsck - BTRFS cannot fix itself * raid - BTRFS raid currently cannot repair itself and current git of the latest linux kernel still has these isses as well as space issues. I wouldn't trust BTRFS to store /dev/random

Good, because it's an experimental filesystem. Don't write it off completely though, because all of those (except for "cache layer" -- wtf does that even mean?) are planned.