Am slowly changing the composition from 100% to about 50% milk, and then taste dependent, will work down to all water eventually (or at least find out what the lowest % milk with taste impact is).
I use one serving (1 cup) of the fat free Hood Calorie Countdown milk for mine, and it makes a huge difference over water. And the numbers are really good:
Here's my latest recipe:
1/2 cup skim milk
2 scoops choc. whey
1 tbs. Hersheys Special dark cocoa (only 12 cal.)
1 tbs. espresso powder
Shake it up and add to about 12oz. of coffee. Enough for 2 servings. For the whey I use, its 54g of protein, 6g carbs, 0 fat, and 340 cal.