If you've been waiting (as I have) for Dedup capability in ZFS, then the wait is close to over. See Jeff Bonwick's blog: http://blogs.sun.com/bonwick/en_US/entry/zfs_dedup
I can't wait to test it, as soon as I can find out how to get my hands on it, lol. It's not in Sol10 update 8, nor is it in the most recent snapshot of OpenSolaris, but I suspect it will be out soon.
Seems my rss feed is slow. It's currently in OpenSolaris, as of last night!