I dig using lactose because it adds a little twang and mellowness to the beer. I used to keep my milk stouts and coffee stouts as separate recipes, but an experimental batch quickly changed my mind. Seems all my good recipes were accidents at their inception. If you're looking for an awesome example of a big coffee stout, try to find a bottle of Terrapin Wake 'N Bake. Sweet mother of wort that stuff is amazing. That one is sans lactose though.