If one cup is too few, and 3 1/2 cups is way too many, I think my ususal two is just right.
We made a run to the store to get coffee filters after the hour and a half we spent at AC Moore getting my b-day present. (total LACK of customer service, btw) We got home late, and went to bed even later. So Saturday I over did it and had 3 1/2 cups of coffe - and then I had the shakes. That didn't make my day any easier. So I'm sticking with two cups and making sure to never run out of filters again.