Originally Posted by Alix
You bet it is. The only difference will be the texture of the final product. Butter melts quicker than shortening so the brownie will likely be denser. I personally use butter only in my brownies. Yum! You have me craving them now! Welcome to DC.
Butter also has a better flavor, of course.
Works the other way, too -- you can generally substitute shortening for butter in most recipes, if you don't mind the loss of flavor. I seem to recall reading that shortening makes for crisper cookies, but I can't swear to that because I've never done any side-by-side comparisons.