On this particular server, it's just a backup destination dump so the CPU use isn't a big deal.
Also have dedup turned on and active for an accounting server. So far, there have been no issues with CPU time/utilization that would effect business. Windows actually handles it well and it hurt to say that. So no NOTICEABLE load.
Of course you could always schedule your deduping task for off peak hours if it is causing performance issues.
The only other deduping I have got to use were for 'Greenbytes' storage devies. These had a backend powered by BSD and used a ZFS filesystem. Definitley more enterprise class with snapshot support.
Will definitely take a peek at SolidFire...