You can also access the loads by checking through amadeus or sabre, by checking the airlines when they flash the remainder of their seats by fare class. (I.E J.C.Y.M.B.H.V.Q.L) etc etc etc......this thing is very accurate, but for the sake of people trying to get a visual on anticipated loads, please do not over-use the system, sooner or later, they will get the idea..
If you work for Delta, you can check the loads of the flights via the extranet/intranet (travelnet) or via the travelnet hotline... tells you exactly how many seats are available... don't know of any other way unless you have access to the res system.
Yes you could sit at the gate and watch, but that isnt goingto tell you anything other than what was happening on that day, would not tell youwhat was happening on other days. I don;t know if it was proven or not, but I think it was either that or they had inside information