I am brewing my Coffee Porter at this very moment.
I have not tried mashing as beans, but I would suspect that it is not the most efficient way, lacking grind, time and temperatures. Anyone else has tried this?
Boiling beans yielded very poor results, extremely acrid and bitter. Undrinkable. Turns out the ideal temperature for brewing coffee is 205F, anything higher than that brings those terrible flavors.
Boiling with coffee works, and yields far better results than boiling with beans. However, I have found that I loose a fair amount of coffee aroma that I am looking for, as most of those aromatic oils are boiled off.
I use coffee in secondary. I put whole beans in a nylon bag and leave it for several days until the flavor and aroma are where I want them. A friend of mine does a cold extract in a French press for 24 hours with a course grind, and then blends it when he is kegging. Both of these methods seem to work very well, yields less acidity, and better aroma.