Your actually not far off. The power users are mostly just businesses and government offices. I know because I work for a major print company in my area and we actually have a mail department in our building that uses the Post Office 3-5x per day, not including our own delivery service, fed-ex, ups, etc. We also work with a lot of other businesses in the area and government print work, and use the PO constantly. During our Political Season, they will actually cut us off after a point and simply tell us they can only send so much mail by a certain date.