From The Rodale Book of Composting;
"The nutrient content of coffee residues varies according to the type of residue. Grounds have up to 2% nitrogen, 0.33 % phosphoric acid and varying amounts ofpotassium. Drip coffee grounds contain more nutrients than boiled grounds, though the potassium content is still below 1%. Other substances found include sugars, carbohydrates, some vitamins, trace elements and caffeine.
Coffee processing plants sell coffee chaff, a dark material containing over 2% nitrogen and potassium. Chaff is useful either as a mulch or as a compost. Apply your coffee grounds immediately, or mix them with other organic matter. They hold moisture extremely well. Left standing, they will quickly sour, inviting acetobacters (vinegar-producing microbes) and fruit flies."
How cool is that! My coffee not only gets me going, but is healthy and helpful for my compost and plants too!