Data Deduplication is a big deal, as was shown back in July when EMC spent 2.4B$ to acquire Data Domain.
This morning Jeff announced that dedup has been added to ZFS;
this has generated quite a bit of buzz in the 'web, although I've yet to see
Oracle's stock going up...
changing their mind.
Check Jeff's post and
comments; it is a nice read.
Also read on disk savings at ZFS-Discuss.