http://www.reefkeeping.com/issues/2005-01/hcs3/
Up to 20 inches long and will eat any fish that will fit in its mouth. May eat ornamental shrimp. Your coral is safe though. Some sources say 24 inches long though if obtained smaller won't achieve that length in an aquarium.
I've seen various fusiliers at my lfs, and they're very pretty as juveniles (albeit large enough to look like adult fish to those not aware). I've also seen larger ones, and they are not so pretty. They always look dull and like they just don't belong in the aquarium. Very large fish to attempt to keep in a home tank!