I've been using Zevo's ZFS since December. I've had dedup enabled (2TB ZFS, 24 GB, so RAM was not an issue) in the past but disabled dedup at one time and thought that performance then would be fine.
Even though I thought that after disabling dedup the system would go back up normal speed, it did not. Performance and Scrub on the drive were really slow and the whole system sometimes hung for minutes.
The pool consisted of 2 mirrored 2TB drives. I've ripped out one disk and copied (zfs send -R) the whole pool to a new pool on the second disk without dedup. Now speed is much much higher. A Scrub now takes only hours not a couple of days.