I take 200 mcg per day in capsule form. But a better way to get it, which I also do, is through Brewers' Yeast, which gives you 190mcg of Chromium (not to mention selenium, potassium, choline, zinc, magnesium and a wide array of amino acids).
The article Loco posted reflects my understanding. Its advised to have sufficient amounts to support your efforts. But its not a miracle substance as many have touted it.