ZFS pool revision 28 has been recently imported into FreeBSD 9-CURRENT. Among others, things to enjoy:

• Data deduplication
• RAID triple parity -- RAIDZ3
• zfs diff command (describes differences between snapshots)
• zpool split command (splitting mirrored pools)
• Snapshot holds (e.g. keeping old snapshots when receiving from a source that removed them)
• zpool import -F (allows to rewind corrupted pool to earlier transaction group)

Expected merge into 8-STABLE: in one month.