It's simple. For AA or any other airline Take the amount of the fare and divide by the number of (round-trip) miles. If the fare is below .02 cents miles, then you're in the ballpark.
The definition of a 'mileage run' is pretty far reaching - I would say any air trips that are meant to maximize miles and/or segments for the sole purpose of gaining FF miles and/or STATUS is considered a mileage run.
Sometimes it's a simple as scheduling a flight with a connection instead of a direct flight (i.e. flight on CO from EWR-DEN is 3200 miles direct, if I connect through IAH I tack on an extra 1000 miles), taking an extra trip at the end of the year so you have the miles or segments to get elite status, or you can be certifiably insane like B747-437B's example
Hey Sean, were you able to give away all of your first class upgrades? How were the reactions?