I always use a refractometer for checking final gravity (and starting gravity), and it's been spot on with the appropriate calculations. I've even checked it against a final gravity hydrometer (shorter scale than a regular hydrometer), and their readings agree.
On Deck: Jamil's Vanilla Robust Porter
Fermenting: Orange Blossom Mead
Kegs: Element 56 Pale Ale, Ron's Belgian Blonde, Summer'n Saison, Furloughktoberfest '09, Grateful Pale Ale, Sam Adams Cream Stout Clone, EdWort's Apfelwein